Resources
Resource 1: Sources of difficulty in the electricity topic
This resource is used in Activity 1.
| Section | Activity | Key teaching points/What do I want students to learn from activity and related text? | Sources of difficulty? Possible misunderstandings? |
|---|---|---|---|
| 12.1 | – | Current (measured in amperes) is the flow of charge (measured in coulombs) per second. Current measured by an ammeter. Conventional current flow is from + to – Current and electron drift through a conductor. Current is instantaneous but drift speed is about 1mms–1 | Charge not something that is visible Confusion over electron flow direction and conventional current Reconciling slow drift of electrons with instantaneous current |
| 12.2 | – | Potential difference across a conductor makes charge move through it Potential difference = work done per unit charge 1 volt = 1 joule per coulomb measured using a voltmeter | Idea that a battery provides current rather than voltage |
| 12.3 | – | Conventional symbols for commonly used components | – |
| 12.4 | 12.1 | Voltage and current relationship for a conductor. Ohm’s Law derived from graph of V vs I for different numbers of cells | Residual confusion between voltage and current Relating circuit diagram to real circuit construction Voltmeter and ammeter connections |
| 12.2 | Changing the component affects the current. Concept of resistance: increasing resistance gives lower current | Possible ‘current is used up by components’ misunderstanding Mental model of electrons moving through a conductor used in text discussion | |
| 12.3 | Factors affecting resistance of a conductor The greater the resistivity or length of wire, the greater the resistance The greater the cross-sectional area, the lower the resistance | Measuring current and inferring resistance – not measuring resistance directly. To derive cross-sectional area rule, need to remind students that doubling the diameter quadruples the area Remembering relationship | |
| 12.5 | 12.4 | For resistors in series: current the same anywhere in a series circuit; current depends on the total value of the resistance | Relating circuit to circuit diagram – ‘current used up’ misunderstanding |
| 12.6.1 | 12.5 | For resistors in series, total potential difference is sum of potential differences across each resistor. As V = IR, combined resistance of resistors in series = sum of individual resistances | Relating circuit to circuit diagram |
| 12.6.2 | 12.6 | For three resistors in parallel, pd across each resistor is the same as the pd across the combination Current though undivided part of circuit = sum of currents through each resistor | Relating circuit to circuit diagram Measurements could be confusing to follow Derivation of total resistance that follows activity could be challenging; idea of reduced total resistance is at first counter-intuitive |
| 12.7 | – | Some energy is dissipated as heat when a current flows through a conductor Power P = VI Energy H = V I t Energy | |
| 12.7.1 | – | Practical applications of heating effect: heaters, toasters, etc., filament lamps, fuses | Will all students be familiar with all of these examples? |
| 12.8 | – | Electric power P = V I I P = V/R Power is measured in watts Commercial unit of energy = kilowatt hour (kW h) = 3.6 × 106 joules. Charge is not used up by electrical equipment. We pay for energy used, not charge | Confusion between energy and charge |
4 Summary