Module 3: Secondary Science - Physics

Theme: Probing students’ understanding

Introduction

At the end of teaching a topic, teachers usually set a test or an exam to find out what their students have learned. They are often dismayed to find that it is not as much as they expected but by this time it is too late to help students. A good teacher will find out what students understand as they go along and what the students are finding difficult and help them to make progress.

This unit has three short activities that will fit into your normal teaching about properties of matter and will show you how to find out what your students understand. Don’t worry – the activities won’t prevent you from finishing the syllabus; they are fairly short and will help your students to learn. Once you have tried these activities, you will be able to adapt them when you teach other topics.

Questioning

Good questioning is really important and is not as simple as it first may seem. It can help you develop good relationships with your students, it can help your students to organise their thoughts and therefore help them to learn, and it can provide you with valuable insights into their thinking. Good questions can promote thought, encourage enquiry and help with assessment.

By thinking carefully about the sorts of questions that you can ask, you will improve your teaching.

It is helpful to think of questions as being ‘open’ or ‘closed’ and ‘person’ or ‘subject-centred’.

Closed questions have a single correct answer. They can reassure students and help you to find out what they remember. But too many closed questions can limit the opportunities to explore thinking and develop understanding. They are often undemanding and can be quite threatening if the student lacks confidence.

Open questions have no right answer, or several right answers. They give you opportunity to find out what your students are thinking, and can be less threatening for some students.

Subject-centred questions ask things like ‘what goes into a plant?’ and ‘what sort of rock is this?’

Person-centred questions focus on the student and are less threatening and more learner-friendly: ‘What do you think goes into the plant?’ ‘What do you notice about the rock?’

A committee of educators chaired by Benjamin Bloom devised a taxonomy of types of questions in which they identified ‘lower order questions’ and ‘higher order questions’. Research shows that lower order, recall-type questions tend to dominate classrooms. This leads to an emphasis on remembering facts and reduces the opportunities for creativity, thinking and developing understanding (see table).

It is important that you plan your questions appropriately. When you are doing a practical demonstration, for example, or introducing a new topic, write out a list that includes some lower order and some higher order questions. This way, you will be using questions to help your students to learn. Just like every aspect of teaching, you need to practise! You also need to think about how you respond to your students’ answers. Try and give them time to think, ask several students the same question or let them discuss the answer before they respond.

Conventionally, students are asked to put their hands up when they answer a question. You probably find that the same students frequently put their hands up and some do so very rarely. It can be very effective to ask specific students to answer your questions and not to ask them to put their hands up. Everyone will have to listen as they know that they might get asked. When you first start doing this, make sure that you direct easy questions at students who you know will find the work difficult. If they can successfully answer some of your questions, they will become more confident.

Corn starch and water – a curious mixture!

Your students will probably be familiar with the properties of solids, liquids and gases. They will be able to describe their properties and, classify a substance correctly on the basis of its properties. This is fine so long as a particular substance falls neatly into one or other of the categories. But what happens if it doesn’t? You have seen, for example, that sand, though composed of tiny grains of solid behaves, in some ways, like a liquid. Only one individual grain on its own would satisfy all of the criteria for a solid.

So some substances are definitely difficult to classify. However, you can use this as an opportunity to probe your students’ understanding of the nature of solids, liquids and gases. In this activity you will make a substance that is difficult to classify. The substance is made from water and cornstarch. In order to experiment with it you will need the following materials:

• One box of cornstarch, 450 g (16 oz), or equivalent (a powder with a high starch content)
• A large mixing bowl
• A jug of water
• A spoon
• A large plastic food bag
• Newspaper or similar to cover the floor
• Water
• Food colouring
• A cup or beaker.

Method

• Pour approximately ¹/₄ of the box (about 100 g, 4 oz) of cornstarch into the mixing bowl and slowly add about ¹/₂ cup of water. Stir. Sometimes it is easier (and more fun) to mix the cornstarch and water with your bare hands.
• Continue adding cornstarch and water in small amounts until you get a mixture that has the consistency of honey. It may take a few tries to get the consistency just right, but you will eventually end up mixing one box of cornstarch with roughly 1 to 2 cups of water. As a general rule, you're looking for a mixture of approximately 10 parts of cornstarch to 1 part water. Notice that the mixture gets thicker or more viscous as you add more cornstarch.
• Sink your hand into the bowl of cornstarch and water, and notice its unusual consistency. Compare what it feels like to move your hand around slowly and then very quickly. You can’t move your hand around very fast! In fact, the faster you thrash around, the more like a solid the mixture becomes. Sink your entire hand in and try to grab the fluid and pull it up. That’s the sensation of sinking in quicksand.
• Drop a small object into the cornstarch mixture and then try to get it out. It’s quite difficult to do.
• Slap the surface of the mixture hard. If you have used just the right proportions it will not splatter all over the place as you might have expected.

Explaining the properties of cornstarch ‘quicksand’

Cornstarch mixed with water is an example of a heterogeneous mixture. That’s a bit of a mouthful! Basically it means that both components of the mixture can be seen in the mixture, or they could be if the particles of cornstarch were not so small. Over time the particles settle out and sink to the bottom so do not pour any remaining mixture down a sink – the water will evaporate and leave a solid lump of matter that will block it.

In fact the cornstarch and water mixture acts like a solid sometimes and a liquid at other times. The mixture is in fact an example of a suspension – a mixture of two substances, one which is finely divided (the solid) dispersed in the other (the liquid).

When you slap the surface with your hand you force the long starch molecules closer together. It feels like a solid. This impact traps water molecules between the starch chains and forms a semi-rigid structure. When the pressure is released, the cornstarch flows again.

If you push your finger slowly into the mixture, it goes in easily and it feels like a liquid.

All fluids have a property known as viscosity – or resistance to flow. The more resistance to flow a liquid has the greater its viscosity is; e.g. honey,. Water has a low viscosity. Sir Isaac Newton proved that viscosity is affected by temperature. So, if you heat honey, its viscosity is less than that of cold honey. Cornstarch, water mixtures and quicksand are regarded as non-Newtonian fluids because their viscosities change when a force is applied, not when heat is applied.

Some examples of materials that are harder to classify

Some materials appear to be a single substance but aren’t:

• Sand (or powders, like flour). This flows (like a liquid) but is made of tiny bits of solid. There is air in the gaps between the sand particles.
• Modelling clay (e.g. ‘plasticine’) is a mixture of a solid and a liquid. It loses its oil as it gets older, and becomes, dry, hard and unworkable.
• A cloud floats in the air (like a gas) but is composed of many tiny droplets of water in air.
• A jelly is a mixture in which small amounts of a liquid are mixed into another material which is a solid.
• Toothpaste is a mixture in which there are small amounts of a solid mixed in amongst another material which is a liquid.
• A foam is a mixture in which there is a gas mixed into another material which is a liquid.
• A sponge is a solid with air or liquid mixed with it. As a result it can be compressed, unlike most solids.
• Some liquids (like tomato ketchup) are thick and do not flow very well, but if you shake them, they become thinner and flow easily.

Set of statements about solids, liquids and gases

Answers for teachers

Solid: 1, 5, 7, 11

Liquid: 3, 4, 8, 10, 14, 15

Gas: 2, 6, 9, 12, 13, 15

Students’ writing

Getting students to write about their ideas is a good way to find out what they understand. Traditionally most of the writing that students do in science involves writing short answers to closed questions, or copying notes from the board. If this is all the writing that your students do, then you will be missing opportunities for them to demonstrate what they know and to be creative.

Writing in science should definitely not be restricted to answering questions and copying notes. There are a variety of ways in which you can use children’s writing to probe their understanding, develop their knowledge, motivate them and refine their skills. Some of these are summarised below.

DARTS

This stands for Directed Activities Related to Texts. As the name suggests the activities involve pupils working with texts that have been changed in some way. These activities provide a good alternative to simply copying off the board as the students will have to think about what they are writing.

One common approach is to provide some text with words missing. The students have to fill in the gaps. The missing words can be listed below, or not, depending on the abilities of the pupils. The first letter of the missing words can be supplied, which makes it a bit easier.

Other approaches are as follows:

• Sentences that link together to explain a process or phenomenon can be jumbled up and pupils have to decide their correct order.
• Sentences that have to be completed in order to provide complete definitions.
• Diagrams are provided which students have to label.
• A table is provided with some gaps to be filled in.
• A piece of text is provided in which students have to underline key words or definitions.
• A piece of text is provided and students have to use it to make a table or a diagram or produce a summary.

Word matching

You supply a list of scientific words, and definitions. Students have to match the right word with the correct definition.

Experiment write up

Encouraging your students to write about their experiments in their own words will show you how much they understand. A strategy that teachers often use is to provide some headings and some key words that their students should be trying to use so that they can structure their writing.

Concept map or mind map construction

This involves breaking down a complex idea, or process, into sections and linking them graphically to display their logical sequential relationships and how they contribute to an understanding of the whole. This is normally quite difficult and needs a lot of practice. Probably more significantly it requires a sound knowledge of the subject if the maps are to make sense.

Writing for different audiences

This sort of writing sometimes helps students who find science difficult, but who enjoy humanities. Examples include:

• Producing a poster. This will not only give pupils an opportunity to demonstrate their knowledge and understanding in writing but also enable them to use drawings and diagrams to illustrate science concepts.
• Producing an information leaflet on a particular topic that could be used by younger children.
• Writing a letter or a newspaper article to express a point of view. For example, arguing for an issue which involves explaining some scientific background such as vaccination, or preventing HIV.

Expansion of a solid: ball and ring

When both the ball and ring are at room temperature, the ball can be dropped through the ring. Heating the ball makes the metal expand, so it cannot pass through the ring. As the ball cools down, it contracts and will fit through the ring again.

Key words: solid, heating, cooling, expansion, expand, contraction, contracts particles, vibration, vibrate, energy

Expansion of a liquid: model thermometer

Fill a boiling tube with coloured water, then insert a narrow glass tube (inserted through a cork or bung) into the neck of the boiling tube: make sure the end of the glass tube is in the water. As you heat the water in the boiling tube, you should see the column of coloured liquid in the glass tubing get higher and higher, because the liquid is expanding as it is heated. This is how liquid-in-glass thermometers work.

Key words: liquid, heat expansion, expands, particles, movement, energy

Expansion of a gas: liquid in a tube/bubbling flasks

You can show this by using a test tube or boiling tube with a piece of capillary tubing inserted into it through a bung. The capillary tubing should have a very small amount of water in it. If you warm the tube with your hands, you should see the water rise up the tube: it is being pushed up by the air which is trapped inside the test tube.

Another way to do this is to use a boiling tube or round bottomed flask with a narrow glass tube inserted into it. Clamp the tube or flask so that the open end of the glass tubing is below the surface of a trough of water. When you warm the air in the flask with your hands, bubbles of air will come out of the tubing into the water.

You can demonstrate the opposite process – contraction of a gas as it cools – if you have an empty plastic drinks bottle with a screw top. Pour some hot water into the bottle, swirl it round, then pour it out again. Screw the top back on straight away. Leave the bottle to cool down and watch as it collapses (because the cooling air inside contracts).

Key words: gas, heating expansion, expands, contracts, contraction, particles, collisions, energy

Dissolving and diffusion

Potassium permanganate crystals in water

Get a glass trough, or a large glass beaker or glass bowl and put water in it to about 10 cm depth. The container must be on a steady surface, and give a good view of the contents either from the side or from above. It helps to have some white paper under the container and behind it, so it will be easier to see any colour changes in the water. Let the water settle completely, then drop one or two (no more) potassium permanganate crystals into the water. The colour spreads out slowly from the crystal and the crystal gets smaller as it dissolves in the water. Purple colour is evidence that there is some potassium permanganate in that bit of the water. If left long enough, the purple colour will spread throughout all of the liquid and the colour will be the same intensity, instead of being deepest near the crystal. The slow colour spreading is evidence of diffusion.

Key words: potassium permanganate crystal, solid, dissolving, dissolves, diffusion, particles, collisions, random

Perfume in air

Spray some strong perfume in one corner of the room. Ask your students to put their hand up when they can smell the perfume. The perfume particles will diffuse through the room, with the people nearest to where it was sprayed, smelling it first. Comparison with the potassium permanganate experiment shows that diffusion is faster in gases than in liquids.

Key words: diffusion, particles, collisions, spaces, random

Theme: Making science practical

Introduction

Organising practical work is an important part of being a science teacher. Gaining first hand experience of materials, organisms and processes can increase understanding and assist retention of knowledge. Shared experiences and real objects may also be helpful for students who find English difficult. All practical work requires careful planning and some improvisation.

In this unit we take the topic of measurement and illustrate three different ways of organising practical work: demonstration, a laboratory parade and solving a problem. Some of the ideas in this topic are demanding and in your class you will find that some students race ahead, whereas others find the ideas difficult. We have used these activities to show how you can differentiate the work and cater for students of all abilities. You need to be able to support those who are finding the work difficult and challenge those who are capable of taking it further. Resource 1 provides some ideas about the different ways of differentiating work.

Differentiating work for students of varying abilities

As you will, of course, understand, each pupil has different abilities. There can also be a significant difference in age between the oldest and youngest pupil in the class. Some students will learn more effectively by reading a book, some by carrying out a practical activity and some by listening to and absorbing spoken instructions. Some will understand the work very easily, some will take more time. Some will work very quickly through any task you set, some will work slowly. It is impossible for you as a teacher to take all the differences into account all the time, but there are things that you can do to support individuals within a class.

If you have a class of 30 or more pupils this might sound like a daunting task! There are two important things that you need to do to be able to effectively cater for everyone in your class:

1. Know your students. You need to give them opportunities to work in groups and listen to the conversations; you need to mark their written work; you need to ask questions of individuals in class and you need to encourage them to ask you questions if they don’t understand or just want to know more. When you know who understands easily, who finds science difficult, who likes to talk, who likes to write, who likes to draw and who likes doing experiments, you will be in a much better position to help individuals.
2. Know your subject. It is unrealistic to expect everyone to remember and understand everything that you do. Students who find science difficult will be overwhelmed if you try and tell them everything. You need to break each topic down into simple steps and make sure that everyone understands the most important ideas.

You can cater for the range of abilities within your group in two main ways:

Differentiating by outcome

This can involve providing a set of questions that get progressively more difficult. Everyone gets as far as they can. Alternatively, you can set open-ended tasks in which students demonstrate what they can do. This also gives you the opportunity to give them a choice about how they present their work, which can be very motivating. You may find that the degree of support that you need to provide to individuals, pairs or small groups within the class varies significantly.

Differentiation by task

This involves setting different students, or groups of students different tasks. For example, in a practical session some pupils could have instructions provided for them in written form and some could have them in diagram form and some could have a combination of both.

You could provide a set of questions that cover the basic ideas that you judge that everyone needs to understand and a set that are more challenging. The students who you expect to get a grade A could be given the more challenging ones.

Learning style

There is a lot of research that suggests that different students prefer to learn in different ways. The three learning styles that are more commonly referred to are visual, audio and kinaesthetic, i.e. some students prefer diagrams and pictures, some learn best by listening and some prefer to be able to do things.

As a teacher you cannot be expected to cater for all the students all the time, but a good teacher will make sure that their lessons contain activities that cover all three learning styles.

There is a tendency to expect students to do a lot of listening. You should make sure that your students also get to do experiments or activities that involve moving around the room and talking about the science. Encourage them to use mind-maps and diagrams or pictures to summarise key ideas, rather than simply copying not

Practical work

Introduction

Practical work is an important part of learning about science and learning to be a scientist.

The TESSA materials consider practical work in science involves pupils finding out, learning and verifying through observation and experiment, using skills and methods that are used by scientists in the real world. There are different types of practical work, which serve different purposes. Over time, a good teacher will make sure that their students experience different types of practical work.

Purposes of practical work

Different types of practical work and particular experiments will meet different objectives, but the benefits of practical work include:

• Developing practical skills and techniques such as how to use a microscope.
• Gaining first hand experience of materials and processes that may increase their understanding of science and help the retention of knowledge.
• Developing inquiry skills, such as control of variables, analysis and recording of data and looking for patterns.
• Motivation and enjoyment.
• Encouraging and promoting higher levels of thinking. Pupils can be asked to predict and explain when presented with problems and phenomena.
• Communication skills. Practical work may provide a context for the development of communication skills. The link to shared experiences and real objects may be very helpful for learners with limited proficiency in English.

Types of practical work

• Demonstrations – A teacher may decide to do a demonstration for reasons of safety or due to lack of time or resources. They may also be the most suitable method for consolidating understanding or providing challenge. Try to actively involve pupils through questioning or through participating in conducting the experiment or activities before or during the demonstration (e.g. predicting if statements are true or false and then using observations to confirm or change their decision).
• Structured practical – Pupils do an experiment in groups. The teacher may give them instructions to follow, advice on recording and analysis and questions to help them relate their observations to theory. These may be suitable for practising skills and techniques, supporting particular inquiry skills, and gaining experiences.
• Rotating (circus) practical – Pupils in groups move from one experiment to the next at ‘stations’ in the classroom. The experiments should be related and instructions should be brief. Similar questions at each experiment will help pupils gradually build their understanding of a key concept, e.g. particle theory of matter or adaptation. Some of the stations may include a card sort or problem to solve rather than an experiment.
• Investigation –Pupils plan, carry out and analyse their own experiment. They may have freedom to choose what they investigate or the teacher may limit the materials available or specify a topic to investigate. The teacher has a role as a facilitator rather than teacher. They will usually give pupils guidance on ‘the scientific method’ or carrying out a ‘fair test’.
• Problem solving – this is similar to an investigation, but pupils have more freedom of approach. It may be a practical problem, such as dropping an egg from the top of a building without breaking it, which can be solved in a number of ways. This can be motivating and a good vehicle for the promotion of communication skills.

Organising practical work

Whenever you are planning an experiment, you should try it out yourself before the lesson. Simple experiments are often more complicated than you might think. You will also need to do a risk assessment. This means thinking about the potential hazards and taking steps to reduce them.

When dealing with chemicals other than water, students should wear safety goggles. If safety goggles are not available, you need to use very dilute solutions (0.1 M). The chemical that is most likely to cause permanent eye damage is sodium hydroxide (above a concentration of 0.4 M).

You will need to think about how your students will get the apparatus they need. The things you might consider could include:

• Give them an activity to do at their desks and, while they are doing it, you distribute the apparatus they will need.
• Spread out the different items around the room and ask one person from each group to collect what they need. By spreading it out, you will avoid the potentially dangerous situation of lots of people gathering in the same place.
• Give out the chemicals yourself with a teaspoon on to small pieces of paper that they can take back to their place. This will ensure that they get the right amount and will avoid a lot of mess!

Examples of measuring equipment and questions

Here are some general ‘prompt’ questions you could ask pupils about pieces of equipment they don’t recognise:

•  

  • Can you see any unit names on it? Or maybe just a letter? What does it stand for? What do we use that to measure?
  • Does it look like something you could make electrical measurements with? Could you connect electrical equipment to it?
  • Are there any knobs you can turn? What happens when you do that?

You could make this easier for students if you make a table of quantities, units and abbreviations for pupils to refer to, here is an example:

Examples of stations for Activity 2

Note: If you have a camera (or a mobile phone with a camera) it would be useful to take photos of pupils as they carry out some of the activities. Look out for really good technique to praise, such as reading a measuring cylinder at eye level, but also try to catch some of the variations in how different people interpret an activity (e.g. Station 6 extension or dragging the load in Station 7).

Station 1

Equipment and notes

Circuit set up with three bulbs connected in series (with a switch in series) to a low voltage dc supply or battery pack providing about 4 V. The voltmeter should be correctly connected across the three lamps using two leads, but the switch to control the supply to the circuit should be left open for students to close themselves.

Instructions for pupils

Close the switch and record the reading in volts.

Station 2

Equipment and notes

Top pan balance or kitchen scales;

Mystery object such as a 20 g mass, or a pebble, in a box or bag (so that pupils won’t see what it is and guess the answer).

Instructions for pupils

Place the bag (box) on the scales and record the mass.

Stations 3, 4 and 5

Equipment and notes

Stations 3 and 4 need identical small blocks of wood, about 2 cm thickness, but provide a ruler for Station 3 and provide a micrometer for Station 4;

Station 5 needs a small piece of sponge about 1 cm thick, plus either a ruler or a micrometer. All three stations need a small diagram to show which dimension pupils should be measuring.

Instructions for pupils

Measure the thickness of the object.

Station 6

Equipment and notes

Measuring cylinder or measuring jug with some water in it. Check that the water level hasn’t been changed after each group. Provide a cloth for mopping up any spillages.

Extension 1: A second measuring cylinder and a pebble to measure the volume of. Students could either lower the pebble into the measuring container and note the change in volume, or use the measuring equipment to collect and measure the water which runs off from a displacement can.

Extension 2: A third measuring cylinder and a collection of 10 small stones (pebbles/gravel/shingle, all roughly the same size and each less than 1 cm across). For this, students will need to adapt the method used for Extension 1. One stone alone will not displace much water, but, students could find the volume displaced by 10 and then use that value to get an average for 1 stone.

Instructions for pupils

How much water is in the container? Record the volume of water in the container.

Extension1: Find the volume of the pebble. (Hint – the pebble displaces its own volume of water).

Extension 2: You have 10 tiny stones. Find the volume of 1 stone.

Station 7

Equipment and notes

2 x Force meters (spring balance): one of them (A) should be hanging from a stand, ready to attach the load, the other (B) should be left on the bench;

A small heavy object to attach to the spring balances.

Watch out for students ‘dropping‘ the load onto the hook so that it falls off or bounces.

Make sure that both force meters are correctly zeroed at the start of the session. You add another aspect to the discussion by using a third force meter (C), set up like the first one but with the screw adjusted so that the ‘zero reading’ isn’t zero. Check every so often that no-one has corrected it.

Instructions for pupils

Attach the object to the hook on the force meter which is hanging up. What is the weight of the object in newtons? (Take care: support the load as you hook it on, then move your hand away.)

Now take the load off and hook it onto the other force meter so that the load is resting on the bench. How much force does it need to drag the load slowly and steadily along the bench?

Answers and things to discuss with your students

These stations not only provide opportunities to make measurements of a range of quantities, but also to discuss why measurements can vary:

The circuit in Station 1 gives an opportunity to read a voltmeter. As pupils don’t have to do anything to the circuit other than close a switch, any variations in the readings obtained are probably down to parallax error – where pupils have taken the reading from an angle instead of directly in front of it. If a digital meter is used, pupils can have difficulty with rapidly changing final numbers. If the circuit is left connected for a long time, it is possible that the values obtained will get lower.

The Station 2 activity is again a simple measurement using kitchen scales or a top pan balance. The issues here are the precision provided by the scale itself, and the variation in reading position.

Stations 3, 4 and 5 present difficulty because of learning to use a micrometer. The values for the two pieces of wood should show relatively little variation, but the sponge should show wider variation because the material will compress easily, so it is more difficult to judge when the micrometer is at the correct position before trying to read the scale.

Station 6 uses a measuring cylinder or a jug to measure the volume of water in the container. The issues in this case are to do with the precision offered by the scale on the jug or the measuring cylinder and also how pupils read the scale. The single pebble may result in more variation, depending on the equipment and method used. Pupils will get even more variation if they try to measure just one small stone, but if they calculate an average value from using 10 stones together there should be less variation. (If you didn’t tell them to use all 10 stones, you could also ask how many stones they used for the measurement.)

Station 7 uses force measurements. You would expect the same object to give rise to identical readings when hung from identical force meters, but pupils should find one set of results skewed because the equipment was not zeroed. Dragging the object along the bench is likely to give a very odd set of results, because pupils will have different ideas of how fast to drag it and at what angle they should pull from: some photos would be very helpful here. It is also difficult to pull steadily and to read a scale that is moving, even if it isn’t also changing at the same time.

Examples of questions about all the results

• Look at the results for (Station x): did everyone in your group agree on the value? If not, why was that?
• Which station’s results showed the most variation? Why do you think that is?
• Which quantity did you find it hardest to measure? Why/what made it difficult? Could you have improved your measurement still using this equipment? Could you have improved your measurement if you’d used different equipment?
• Did any station’s results show a steady change in the value (getting smaller or larger as you went down the column)? If so, why do you think that happened?
• Were any results different when you might have expected them to be the same? Why?
• Which measurements were most/least precise? Explain why.
• Which measurements were most/least accurate? Explain why.

Summary of precision, accuracy and variation for the teacher

Why do measurements vary?

1. Variations caused by the equipment or by the way it is used:
   • The scale isn’t fine enough for the quantity you are trying to measure.
   • The equipment produces variations in the reading which aren’t due to actual changes in the quantity being measured.
   • The scale hasn’t been zeroed before taking measurements
   • The measurements are not being taken in controlled conditions (e.g. there are draughts, changing temperatures).
   • Incorrect technique ( e.g. not reading a scale from directly in front of the needle or indicator, or level with the scale marker).
   • Differences in technique/experimental method.
   • The equipment has been damaged.
2. Variations in the quantity being measured:
   • There is natural variation in the quantity – there is no absolute, ‘true’ value, e.g. length of a leaf, diameter of a seed in the sense that if you chose another leaf or seed the value would be different, no matter how carefully you measured it.
   • The value changes with time because of a factor that hasn’t been considered in setting up the experiment (e.g. the length of a wire may change if the load is left on it, a previously desiccated object might show an increase in volume because it has absorbed water from its surroundings, another object might show a decrease in mass because of losing water to its surroundings, water fresh from the tap may be at a different temperature from water which has been standing in a room for an hour or more…).

‘Accurate’ or ‘precise?’

Accuracy is about how close a measurement is to an agreed true value for specified conditions. A measurement is said to be accurate if it is close to the true value.

Precision is about how closely a set of measurements agree. A set of measurements that gives tight cluster of values is more precise than one with a wide variation in values.

The Earth

Diameter = 12,760 km

Radius = 6,380 km

Mass = 5.972 x 10²⁴ kg

Crust = 40 km thick

Distance from the Earth to the Sun = 1. 426 x 10⁹ km

Distance from Earth to the Moon = 384,000 km

The Moon

Diameter = 3,475 km

Radius = 1,738 km

Mass = 7.35 x 10²² kg

Africa

Distance from the most northerly point (Ras ben Sakka in Tunisia) to the most southerly point (Cape Agulhas in South Africa) = 8,000 km

Distance from the most westerly point in Africa (Cape Verde) to the most easterly point in Africa (Ras Hafun in Somalia) = 7,360 km

Height of a tree

• Measure the length of the shadow and compare this with the length of a shadow cast by a metre rule at the same time. Use scaling to work out the height of the tree.
• Measure the length of the shadow and also the angle ϑ from the ground at the tip of the shadow to the top of the tree (Care: avoid looking at the sun!) then use
  • opposite = adjacent x tan ϑ
  • where opposite is the height of the tree and adjacent is the length of the shadow.

Mass of one sheet of paper

Find the mass M of x sheets of paper, then mass of one sheet = M/x

Area of the palm of your hand

Draw round your hand on a piece of squared paper and count the squares.

Volume of a stone

Displacement methods (see Station 6, Extensions 1 and 2 in Resource 4)

Thickness of a piece of paper

Measure the height (h) of a pile of x pieces of paper. One piece = h/x

Mass of a grain of rice

Measure the mass (M) of a pile of grains. Count the grains (x). The mass of one grain = M/x.

You will need to get several people to count the grains and keep checking until everyone agrees.

Pressure exerted by a student

A student stands on some squared paper and someone draws round their feet. The mass (M) of the same student is found in kg.

The force they exert (F) is the M x 9.8 and is in newtons. The area (A) of their feet on the ground is calculated by counting the squares.

The pressure = F/A.

Theme: Science lived – relevant and real

Introduction

Science is all around us. Activities like baking cakes, growing vegetables and mending a bicycle all involve scientific principles. Making connections between the science they learn in school and the things they do at home can help to reinforce the scientific principles that your students need to learn. It might also help them to understand some of the problems that they and their families face. Resource 1 gives some strategies that you can use in order to help your students make these connections. This unit is not restricted to one topic area – we want to encourage you to develop the habit of relating the science that your students learn about to their everyday lives. You will use brainstorming as a technique for helping them to make connections and you will be encouraged to take them outside the classroom.

Students often see science as something that they do at school and not necessarily related to their lives. An effective way of demonstrating that this is not the case is to start with the everyday context and use it to draw out the scientific principles. Asking students about things outside school that are important can get them engaged and interested – especially if some controversy is involved. Most real-life situations are actually quite complicated and it is easy to find yourself talking about chemistry, biology or physics, or even wider issues. This will help to keep your students interested in science and help them to see how science can help them to understand the world.

Making science relevant to everyday life

Possible strategies

Class discussion

Use local examples where possible, but also encourage pupils to draw on their own experience in the classroom.

Practical work

• Use local examples and materials, e.g. hibiscus indicator; local minibeasts for work on classification or adaptation; wood and kerosene to compare calorific content of fuels.
• Give pupils a challenge using scrap materials, e.g. obtain clean salt.

Research projects

Pupils could find information from local newspapers or magazines or interview adults in the community, such as brewers, mechanics or health workers. This could be the basis of a poster, oral presentation or role play.

Making use of the school grounds

Besides the obvious opportunities for ecological investigations, the school grounds are a source of teaching examples in other topics such as corrosion, structures and forces. Take pupils to see them or ask them to find examples or collect data for analysis.

Day visits

Visit local industries, agricultural sites or museums. The effective teacher will link this to classroom work both before and after the trip.

Homework

Ask pupils to write about examples of science around them (e.g. chemical change in the kitchen or forces on the football field) or to bring materials to the classroom.

Writing tasks

Use local issues as a stimulus for creative written work, e.g. a letter to a newspaper or radio script on local environmental or health issues.

Discussion tasks

• Interviews – one child could be the ‘expert’ and the interviewer can ask questions as if they were producing a news item for the radio.
• Pupils come to a decision about a local issue, e.g. health promotion or energy supply.

You should create a file for yourself and keep any newspaper and magazine articles that you find that contain or are about scientific issues. Every time you start a new topic, ask yourself how it relates to everyday life and help your students to make those connections.

Brainstorming

Brainstorming as a class or in smaller groups can help students to make connections between the science they learn in class and their everyday lives.

Brainstorming

Brainstorming is a group activity that generates as many ideas as possible on a specific issue or problem then decides which ideas offer the best solution. It involves creative thinking by the group to generate new ideas to address the issue or problem they are faced with. Brainstorming helps pupils to:

• understand a new topic
• generate different ways to solve a problem
• be excited by a new concept or idea
• feel involved in a group activity that reaches agreement.

Brainstorming is particularly useful for helping students to make connections between ideas. In science, for example, it can help them to appreciate the links between the ideas they are learning in class and scientific theories.

As a teacher, a brainstorm at the start of a topic will give you a good idea about the extent and depth of knowledge already held by the class. It will not tell you about individuals’ understanding, but it will provide a wealth of collective ideas that you can refer back to as the topic progresses.

How to set up a brainstorming session

Before starting a session, you need to identify a clear issue or problem. This can range from a simple word like ‘energy’ and what it means to the group, or something like ‘How can we develop our school environment?’ To set up a good brainstorm, it is essential to have a word, question or problem that the group is likely to respond to. The teacher can gather the class round the board and run the session, or, in very large classes, divide the class into groups. The questions can be different for different groups. Groups themselves should be as varied as possible in terms of gender and ability.

There needs to be a large sheet of paper that all can see in a group of between six and eight pupils. The ideas of the group need to be recorded as the session progresses so that everyone knows what has been said and can build on or add to earlier ideas. Every idea must be written down, however unusual.

Before the session begins, the following rules are made clear:

1. Everyone in the group must be involved.
2. No one dismisses anyone else’s ideas or suggestions.
3. Unusual and innovative ideas are welcomed.
4. Lots of different ideas are needed.
5. Everyone needs to work quickly; brainstorming is a fast and furious activity.

Running the session

The teacher’s role initially is to encourage discussion, involvement and the recording of ideas. When pupils begin to struggle for ideas, or time is up, get the group (or groups) to select their best three ideas and say why they have chosen these.

• summarise for the class what they have done well
• ask them what they found useful about their activity. What did they discover in the brainstorming that they didn’t realise before?

Everyday examples of pressure

Following are some real-life examples of pressure in action:

• If you are carrying a heavy bag, narrow handles or straps cut into your hands and shoulders, but broad handles and straps are more comfortable.
• Narrow heels on shoes sink in further than wide, flat heels.
• Spreading your weight over a larger area stops you sinking in.
• Heavy vehicles that are used on softer ground need to have bigger, wider tyres.
• A sharp knife has a narrower blade edge than a blunt one, and is easier to cut with.
• Nails and tacks have a flat hammering head plus a sharp point to make it easier to hammer into wood, but also puncture tyres.
• Large machines for digging, grabbing or lifting use hydraulic pressure systems.

Below are some everyday items that rely on pressure to work:

• suction pads
• sucking a drink up with a straw
• siphons
• syringes
• bicycle pumps
• water pumps
• hydraulic jacks for lifting cars
• pneumatic controls
• vacuum cleaners.

Examples of physics in action

Places to visit and examples you might see

Some examples of force multipliers

Hydraulic jack:

You use a small force but push further to raise the large load a smaller distance.

Input pressure = output pressure because the pressure is transmitted by oil.

• narrow input piston cylinder with area A1 , small input force F1
• wider output piston cylinder with area A₂, larger output force F₂
• force on output piston

Levers , e.g. see-saw:

Clockwise turning force x distance from pivot = anticlockwise turning force x distance from pivot

Cutting tools e.g. secateurs, shears:

Background information on insulation and keeping water cool

• Energy (heat) is transferred from hot objects to colder objects.
• Anything that is warmer than its surroundings becomes cooler by transferring energy to the surroundings (so they get warmer); anything that is cooler than its surroundings becomes warmer (and the surroundings become cooler) as energy is transferred from the surroundings to the object.
• If you leave something long enough, it will reach the same temperature as its surroundings.
• To keep a hot object hot, or a cold object cold, you have to slow or stop the transfer of energy (heat).
• Energy (heat) is transferred by conduction, convection and radiation.
• Metals are good conductors but plastics, or materials with lots of air gaps like foams or bubble wrap, are poor conductors (or good insulators).
• Using thermal insulation or insulating a hot or cold object means wrapping the object in a material which is a poor thermal conductor.
• The thicker the insulation, the better it works. Don’t leave gaps in the insulation.
• Heat (energy) is transferred through a fluid like air or water by convection currents. Convection currents rise above the heat source as the warmed air or liquid expands (because it is less dense than the air/water around it). As the air or liquid cools it becomes more dense again and sinks.
• Building designs can make use of convection currents to keep the building cool: to do this they allow warm air to rise through the building and escape from the top, drawing cool air in at the bottom.
• Shiny or white surfaces reflect most radiation, while black surfaces are the best absorbers and transmitters. To make use of solar heating you would use black surfaces to absorb as much energy as possible; to keep something cool, you use shiny surfaces (wrap them in foil, spray them with shiny paint) or white surfaces to reduce absorption.
• Vacuum flasks reduce heat transfer by all three mechanisms: the silvered layer reduces transfer by radiation, the vacuum means there is no air to allow losses by convection, and the insulating foam beneath the casing reduces losses by conduction.
• Thick coverings also help to keep cool things cool because it takes more energy to heat up the covering material. This is why buildings with thick stone walls stay cooler than buildings with thin wooden walls – there is more ‘stuff’ to heat up.
• Water has a high specific heat capacity, meaning it takes a lot of energy to raise its temperature, so it keeps the temperature steady for longer: rivers and lakes are slower to heat up than the surrounding land; leaving cold bottles in a bucket of water on the table keeps them cool longer than just leaving them on the table.
• When a solid melts, it absorbs energy from its surroundings but it stays at the same temperature until all the solid has turned to liquid. Changing from solid to liquid (or from liquid to gas) is called a ‘phase change’, and materials which need a relatively large amount of energy to melt are used in cooling jackets for transferring foods or medical supplies without refrigeration. (When used like this, or in the plaster of buildings to help keep rooms cool, they are called ‘phase change materials’ or PCMs for short.)
• When a liquid evaporates, it uses energy from the surroundings to do so, so we can use evaporation to help keep things cool: letting the water evaporate from your skin instead of using at towel to dry yourself makes you feel cooler, and wrapping a bottle in a damp towel helps to keep it cool for longer.

How can we keep water cool as long as possible?

A cold drink straight from a fridge or chiller can be very refreshing, but it won’t stay cold for long!

Work with your partner to design a way of keeping water cold in a hot climate. You will need to make and test your design, then present a report explaining how it works. Your report should include technical terms associated with heat transfer.

The writing frame below may help you. Structure your report by answering the questions:

Introduction and plan

Results and evaluation

Theme: Problem solving and creativity

Introduction

When your students start to look for a job, the qualifications that they have will obviously be very important. However, potential employers will also be looking for people who are creative and who are able to solve problems; they will be looking for people who can think for themselves. The case studies and activities in this unit are designed to show you how you can give your students the opportunity to be creative and to develop their ‘thinking skills’. Some general strategies are given in Resource 1 . You need to think about how you can create an atmosphere of excitement and enquiry in your classroom. If you can do this, students will ask questions and readily contribute their ideas. Students love dramatic demonstrations and amazing and unbelievable facts and will respond to your genuine enthusiasm about the subjects that you are teaching.

Creativity is about the ability to think, not just recall, but to apply, suggest, extend and model and create analogy. You can encourage your students to be creative by setting them open-ended tasks and giving them choices about how they present their work. For example, students who are particularly talented in the humanity subjects and who enjoy writing, might like to write about science in the form of a newspaper article or a poem. That would not suit everyone, so that is why giving students a choice can be very helpful. As a teacher, being creative doesn’t necessarily involve dreaming up new and exciting activities – although it can do! Creative teachers can take ideas from these units or from their colleagues and adapt them for use in different contexts.

Problem solving and creativity

Through being resourceful and engaging and providing variety, you will be able to motivate your students. If you are willing and able to solve problems and be creative, you will be able to help your students develop these skills. And it is not as difficult as it might seem!

Creativity

Creativity is about the ability to think. It is not just about remembering, but also applying, suggesting, extending, modelling, and offering alternatives. It is something that you can model for your students. Students need to be encouraged to think differently and come up with original ideas. They also need to feel confident in the reception they will get before they make such suggestions.

Some teachers will naturally be very creative, but some will not – and that is fine as long as you are resourceful and willing to try new ideas. A creative teacher, for example, will take the TESSA Secondary Science units and apply the strategies we suggest to different contexts. You could use news items from radio, television or newspapers and relate this to the science you are teaching. You can set open-ended tasks and allow students to make choices about how they present their work. You may take some risks in your teaching. Above all, you will create an atmosphere of excitement and enquiry with dramatic demonstrations, enthusiasm or amazing and unbelievable facts.

Problem solving

Helping students to develop problem-solving skills is a frequently cited goal of science teachers. As with creativity, you can model these skills in your own classroom. For example, if you can’t answer a student’s question, you can come back next lesson with a solution and explain how you worked it out and why you found it hard. Being able to solve problems involves developing thinking skills. There are various strategies that you can adopt to help children develop these skills (Wellington and Ireson, 2008):

• Encouraging student-generated questions. The act of asking questions requires engagement and creative thought, two core cognitive strategies.
• Being clear about ‘purpose’. Students should be encouraged to ask: what is this all about?’ ‘What does this relate to?’ ‘Why do you want us to do this?’ – rather than embark on activities in an unthinking, recipe-following fashion.
• Setting open-ended activities. Teachers should set activities that can be tackled in a variety of ways so that children have to think about how they will tackle the problem.
• Planning. Teachers need to provide opportunities for children to plan their problem-solving strategy in a systematic way.
• Paraphrasing. It is well known that you really get to know and understand ideas when you try to teach them to someone else. Giving children opportunity to paraphrase an explanation will help them to understand difficult ideas and to be aware of their own learning.
• Learning to learn (metacognition). Teachers can encourage children to become more conscious of their learning by getting them to think about why they don’t understand and what strategies helped them that might be useful in the future.

Reference

Wellington, J. and Ireson, G. (2008) Science learning, Science teaching. Abingdon: Routledge.

Promoting cross-curricular links and literacy skills

Forces

This resource is for use with Activity 2.

Forces can change the shape of an object, can make it move faster or slower, or change the direction it is moving in.

If an object is not moving, or is moving at a steady speed in a straight line, then the forces on it must be balanced.

The bigger the force on an object, the bigger the acceleration (change in velocity) it produces. If something is accelerating (getting faster while moving in a straight line or moving in a curve) then the forces on it are not balanced.

Forces (and velocity and acceleration) are vector quantities – they have size and direction. (Scalar quantities like speed and mass just have size). We can show them as force arrows, where the arrows are drawn to scale and the length of the arrow represents the size of the force.

Using force diagrams with students

Asking students to draw diagrams of the forces acting on an object – or adding force arrows to an incomplete diagram – is a good way to explore what they think is happening, and to encourage discussion.

Providing pictures for labelling, rather than asking students to draw the objects, can help to avoid the problem of students worrying about their drawing ability or spending all the time making a pretty drawing instead of thinking about the science. The most important thing is for students to use arrows to identify the forces acting on an object and to show what direction they act in.

For older students, you can introduce some additional guidelines:

• Force arrows are straight arrows (not curved ones).
• The arrow should start from the part it is acting on, and points in the direction the force acts.
• The longer the arrow, the bigger the force.
• If two forces are balanced (so the object is either not moving, or is moving steadily) then the arrows will be the same size and start from the same point, but go in opposite directions.
• If two forces on an object are not balanced (so the object is accelerating), then the bigger force will be in the direction it is accelerating, and the arrow for that force will be bigger.

Identifying the forces acting on objects: some examples

Diagram 1 A spring balance with mass hanging from it in air and in water.

The forcemeter in Diagram 1shows that a smaller force is pulling on it when the mass is in water.

The mass hanging from the forcemeter pulls down the spring less when it is in water.

The mass is unchanged: the pull of gravity on it (red arrow, shown on both diagrams) is the same in air and in water, so its weight is unchanged. It appears to weigh less because there is an upthrust force (blue arrows, only on the right hand image) on the mass.

The balloon in Diagram 2 has only a small mass, so the pull of gravity is fairly small. You have to push down to make the balloon go further under water. The further you push the balloon under water, the harder you have to push to keep it there.

As you push the balloon down, you can see the water level rise: the water that you push out of the way (displace) as the balloon goes further under water.

The amount of upthrust depends on the volume of water that is displaced by the balloon.

Diagram 2 Pushing a balloon under water

Diagram 3 A needle floating in water

A needle does not weigh very much, but it doesn’t displace much water as it seems to lie on the surface; so what is keeping it up? There must be enough force pushing back up on the needle to counter the weight (Diagram 3).

Add a drop of detergent to the water. The needle should sink, because it was being held up by the surface tension of the water.

Identifying the forces during a bungee jump

There are three stages to consider:

1. On the way down
2. At the lowest point of the jump
3. On the way back up

1. On the way down, there is no tension in the bungee rope. The most significant force on the jumper is their own weight, due to the pull of gravity. Some students may also suggest air resistance, but this will be relatively small. Air resistance acts on the surface (think of the jumper pushing through the air as they fall).
2. At the lowest point in the jump, the tension in the bungee rope is at its maximum, and is enough to stop them falling any further.
3. The elastic rope pulls the jumper back up: the rope is no longer so stretched, so the upward pull from the tension is less.

Getting students to generate their own questions

For students to ask questions about something they are studying they need to feel that asking questions is a good thing, and that they won’t be laughed at or thought stupid for asking.

Things you can do

You can encourage students to ask questions by giving replies like ‘That’s a good question! What do you think?’, or ‘Shall we find out?’ or ’Hmmm… let’s find out!’.

This raises two important points:

1. It is usually better not to simply give students the answer, but to encourage more thinking.
2. You need to have thought about the kind of questions that students might ask, so you have things ready in your room to try out ideas. This might mean a simple additional practical activity that would help students to understand the point more thoroughly, or might be a way of testing out their predictions, or it might mean using the internet or reference books to see if they have any answers. In the latter case, it is important to ask students to think about what are the key words or questions they might use in a search, and help them to rephrase those suggestions into something useful, rather than telling them what to look for.

Another way of promoting a spirit of enquiry is to have something set up and working, or some unusual items as ‘talking points’, so students can ask you ‘What is that for?’ ‘What does this do?’ and engage you in a conversation about it.

When something unexpected happens, it can make people review their understanding, so it is important to include demonstrations that include something which students will find surprising along with demonstrations that illustrate an important point. It is also important to ask students to predict what they think will happen before they see what does happen, and to be prepared to repeat an activity, so they can get the full benefit from this.

You can show that you value enquiry by being a role model. When something ‘odd’ or unexpected happens, let them hear you wonder why that was, and be ready to look for answers.

Solving problems – thinking about thinking

Here is a challenge!

A lump of Plasticine sinks if you drop it into a bowl of water, even if you lower it in carefully. How can you make the Plasticine float? Can you make it float so well it can carry a small load? How much can it carry?

Try out your idea, then compare your solution with other people’s.

Extending the work on floating and sinking to provide an opportunity for differentiation in a real life problem-solving context

This resource provides an extension to Activity 3.

The context and problem

Recycling is important for saving precious resources when the item can’t be reused any more. Suppose you are trying to recycle waste plastics, how can you sort the plastics into different types so you can sell some of them to someone who can reuse them? (Plastic items have a recycling code on them which tells you what they are made of, but you can’t always see this code on a piece of waste plastic.)

Background information

One method that recycling companies use to sort mixed plastic waste is flotation: different polymers have different densities, so while some will float in a particular liquid (because the polymer is less dense than the liquid) others will sink (because the polymer is more dense than the liquid). If you use three different liquids – water, saturated salt solution and glycerol (propane-1,2,3-triol) – you can sort most polymers.

The common polymers and liquids (shown in bold) are listed here in order of increasing density:

PP (polypropylene), PE (polyethylene), water, ABS (acrylonitrile butadiene styrene), polystyrene, saturated salt solution, PMMA (polymethyl methacrylate, also called acrylic or perspex), PC (polycarbonate – density varies), glycerol, PC (polycarbonate – density varies), PET (polyethylene terephthalate), PVC (polyvinyl chloride).

How the process works

All the plastic waste is chopped up into small pieces before the batch is added to the first tank (water, the least dense of the three liquids). (This is important because the lid and bottle of many plastic bottles will be made from different materials, and because if you use a whole bottle, it has air in it so you are not looking at the density of the plastic but of the bottle.) All the bits that float are skimmed off, and all the bits that sink go into the next tank, and the process is repeated. (Notice that, depending on what was in the original mix, you might have one type of polymer or you might have two or even three polymers in each of the final, separated groups, and you might have to use other tests to work out what bits were a particular polymer: you can’t tell polyethylene and polypropylene apart by this method because they both float in water.)

Setting a differentiated task

You can control the amount of challenge by:

• the way you word the task
• the materials you provide and how you provide them
• the amount of information or guidance you provide.

Some different ways of setting the task

You will need to provide beakers or bowls for testing samples with each liquid. ‘Samples’ should be small pieces of clean plastic. You will also need to provide something to collect items that sink from the bottom of the container, and some cloths or paper towels to wipe up spills, and so students can wipe samples dry before putting them into the next liquid. It works best if you test samples one at a time, or you could leave students to find that out for themselves…

• Provide some identified samples and some ‘mystery’ samples, and ask students to identify the ‘mystery’ samples. This is a simple comparison or matching task.
• Provide some identified samples and ask students to explore which ones float and which sink in each liquid, then make an identification key. The more polymers, the harder the task.
• Provide unknown samples and the information about relative densities, and ask students to suggest what each sample is. The difficulty depends on what samples you provided and what you tell students about them. Deciding if a sample is x or y is easier than identifying with no possibilities suggested.
• Provide unknown samples and the information about relative densities, and ask students to suggest what each sample is and evaluate the method. This adds a different demand because students have to think about what the strengths and weaknesses are. (Was it easy to make a decision about which samples floated each time? What problems are there if you try to test several samples at once? Could they identify all the samples, or only say a sample ‘might be x or y’?)

Some things you could use as sources for different types of polymer

PP       polypropylene: bottle tops, some cosmetics bottles, yoghurt pots, some food trays

PE       polyethylene: bleach or detergent bottles, bottles for still drinks, some cosmetics bottles

PET     polyethylene terephthalate: shampoo bottles, fizzy drinks bottles

PVC    polyvinyl chloride: plastic pipes and cable sheaths

PS       polystyrene: plastic cutlery, ‘foam’ food cartons, drinks cups

PMMApolymethyl methacrylate (acrylic, Perspex): plastic rulers, clear drinks cups.

Theme: Dealing with challenging ideas

Introduction

Being an effective science teacher involves being able to explain difficult ideas very clearly. There are a number of topics in science that are difficult to understand and difficult to explain because the ideas are abstract and based on things that we cannot see. Students often have ideas about science that are ‘wrong’, particularly about the more abstract topics. Just explaining the ‘right’ idea might work in the short term, but often doesn’t last until the student has to take an exam. The ‘wrong’ ideas need to be identified and tackled before progress can be made. Often, simply explaining the ideas is not enough; you need to revisit them and consolidate understanding.

In this unit, the three activities build on each other and will enable you to help your students gradually develop their understanding. The first activity focuses on literacy and making sure that your students understand the key words. The second and third activities use different approaches to developing understanding.

Misconceptions about magnets and magnetism

Researchers have discovered that there are certain misconceptions about electricity and magnetism that are very common. We have summarised them here, so that when you plan your lessons, you can make sure that you address these misconceptions.

Misconception: all metals are attracted to a magnet

Not all metals are attracted to a magnet. Copper, aluminium, gold and silver are all metals, but they aren’t attracted by a magnet. Iron, steel, nickel and cobalt are. Alloys containing these metals can also be attracted to a magnet – ‘copper coins’ attracted to a magnet are not actually copper but a copper–nickel alloy.

Misconception: if something is attracted by a magnet, it is a magnet

Being attracted to a magnet does not mean that a material is a magnet (but it is a magnetic material and can be made into a magnet). If something is attracted to a magnet, turn the magnet round and try again: if the object is repelled by the magnet this time, then the object is a magnet, too.

Misconception: the Magnetic North Pole, i.e. the pole of the earth in the northern hemisphere, is magnetically a north pole

North poles of magnets are the poles that point to the north. Like poles repel, unlike poles attract, so the Earth’s Magnetic North Pole is actually a magnetic south pole, because it attracts the north pole of a magnet!

Misconceptions about circuits and electricity

Misconception: you only need one wire to make a circuit with a battery and a bulb

If students have seen an electric light hanging by a cord from the ceiling or electrical equipment with a lead to a plug, but have never constructed a circuit with batteries and bulbs, then they may think this. (They may also think that if you use two wires, the wire from one end of the battery is the one that counts and the other one is just there as a ‘return route’.) There must be a connection from each end of the battery to two points on the bulb holder (i.e. the metal, not the glass) for the bulb to light.

Misconception: current is ‘used up’ as it flows round the circuit

Current is not used up: the current is the same all the way round a series circuit. If current is used up, then bulbs near the ‘start’ of the circuit should be brighter than those near the ‘end’. Providing the bulbs are identical, then they will all be the same brightness.

Misconception: current starts from one end of a battery and flows through each component of a circuit in turn, until it gets back to the other end of a battery (e.g. battery to wire, then bulb, then wire, then bulb, then wire back to battery)

Current flows instantly in all parts of a circuit when there is a complete circuit. Even if you had a huge circuit going right round the classroom, all the bulbs in it would light up at the same time, not one after the other.

Some key words for electricity and magnetism

Magnets, magnetic materials and non-magnetic materials

Suggested circuits and descriptions

This resource is for use with Activity 2. You can add more of your own that apply to your syllabus.

A circuit with one cell (battery) and a bulb.
A circuit with one cell (battery) and two bulbs connected in series.
A circuit with one cell (battery), and two bulbs connected in parallel.
A circuit with two cells(batteries) and two bulbs connected in series.
A circuit with one cell and a resistor, where one bulb is connected in series with the resistor, and the other bulb is connected in parallel with them.
A circuit with one cell and two bulbs in parallel, with a switch controlling both bulbs. Or A circuit with one cell and two bulbs in parallel, with a switch between the bulbs and the battery.
A circuit with one cell and two bulbs in parallel, with a switch controlling just one of the bulbs. Or A circuit with one cell and two bulbs in parallel, with a switch on one of the branches.

Teacher instructions for role play

Here are two role plays you could use to model what happens in an electric circuit with a small group (for use with Activity 3).

Note: In the descriptions, the different parts of the role play are explained (‘this person is the battery’, ‘this is charge moving round the circuit’, etc.). When you use these models with students, you might decide not to tell them all of this, but just say that this is a role play to model what happens in an electric circuit. Tell everyone in the role-play what to do, then ask them questions like, ‘Who is the battery?’ ‘What represents the moving charges?’ ‘What represents the resistance?’ or ‘How does this show that energy is transferred?’

Sweets and cups

What you need: a packet of wrapped sweets, two boxes, and some paper cups.

What to do:

• Start with everyone except one in a circle. The one outside the circle is an observer.
• One person (the battery) has a box with some wrapped sweets in it: they pass one sweet every second to the person on their right, who immediately passes each sweet to the person on their right, and so on. (It may help to have someone outside the circle keep time for this by tapping the table once a second.)
• One person in the circle has a cup. They represent a lamp or a resistor. When a sweet arrives, they hold it in the cup for a second before they pass it on. Soon, all the sweets in the box are moving steadily around the circle. The observer stands behind the person on the left of the ‘battery’ and claps every time the person they are standing behind passes a sweet back to the battery. The rate the sweets are moving around is the current. Allow the sweets to go round several times, so that everyone settles into the rhythm before you make any changes.
• Now give a cup to a second person, so there are now two lamps/resistors in the circuit. What happens to the rate that sweets pass round the circuit (how often the observer claps) now?
• Now give someone else in the group a box, and half of the sweets. They also pass one sweet a second, so now there are two people passing sweets to the rest of the circle, so there are two sweets a second being passed). This increases the rate that sweets pass round the circle, and the observer claps twice as fast.

This model is good because you can see that the number of charges moving around stays the same. It is also good because you can see that increasing resistance reduces the current. Adding another battery increases the current as you would expect. There is a risk, however, that students will think that adding batteries adds more charges, although you have not got any more sweets moving round than before: focus attention on the rate at which sweets pass the observer. (Alternatively, just keep one person as the battery, but tell them to pass round sweets at twice the rate, i.e., pass a sweet every half second. This is harder to keep up: if you have someone keeping time, then get them to clap at twice the rate they did before.)

Ideally, the sweets would get a little bit smaller every time they passed the ‘lamp’, representing the transfer of energy to the lamp. Eventually, the sweets would be used up – representing the battery running out of energy. This is one feature of an electric circuit that is not represented very well in this model: the transfer of energy from the circuit to the lamp. The second model is better in this respect as students can ‘feel’ the energy as heat is generated by friction.

Rope

What you need: a (large) loop of rope, ideally with a pattern or marks on it every metre, so you can see how fast it is moving round.

What to do:

• Everyone in the group stands in a circle, so that the rope loop is not pulled too tightly, but does not sag anywhere either.
• One person is the battery: they pull the rope around steadily, i.e. with a steady amount of pull. When they pull, the rope should start to move round, and everyone in the circle should feel it move at the same time. The moving rope represents moving charge: charges around the circuit are all moving at the same time.
• Everyone else is the resistance: they grip the rope very lightly as it moves round, to slow it down. As the rope moves through their hands, their hands will be warmed by friction with the rope; and the more tightly the ‘resistances’ grip the rope as it goes round, the more energy is transferred to their hands (beware of sore hands and friction burns caused by people tugging the rope). More grip is meant to slow the rope down, to model how increased resistance gives a smaller current. (This is not a tug of war game: the ‘battery’ is meant to give a constant amount of pull, and should not start pulling harder and harder against the resistance.)

This model is good because it shows that when the current flows around the circuit, the charges are all moving round the circuit at the same time. It also links resistance with energy transfer, and shows that bigger resistance gives a smaller current. However, if the ‘battery’ starts to pull harder to move the rope round, then students might think that adding more resistance will make the battery work harder to keep the current the same.

For each model you should ask the class:

• What forms the circuit in this model?
• What represents the charge moving round the circuit?
• What represents energy in the circuit?
• Where does the current collect energy?
• Where does it give up energy?
• In what ways is this model similar to your own ideas about electricity? In what ways is it different?
• Which model is better?