# Resource 4: Using models and analogies to teach electricity

This resource is used in Activity 2. Table R3.1 identifies models and analogies being used and provides some suggestions for other models that might be helpful.

Table R4.1 Using models and analogies to teach electricity.
SectionActivityKey teaching points/what do I want students to learn from activity and related text?Sources of difficulty?What models or analogies are being used or might help here?
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 1 mm s–1

Charge not something that is visible

Confusion over electron flow direction and conventional current

Reconciling slow drift of electrons with instantaneous current

Being used: Electric current as a flow. Circuit is a continuous closed path – any break stops the flow

Might also help: Rope model

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

Being used: Gravitational potential difference needed for water to flow downhill. Electrical potential difference needed for flow of charge

Might also help: Rope model

12.3Conventional symbols for commonly used components.
12.412.1Voltage 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

Being used: Circuit diagram as representation of circuit (used throughout activities)
12.2Changing 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

Might help: Rope model, sweet model
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

Might help: (Something that could be acted out?) Carrying stacks of parcels in a crowded corridor. Things get knocked off the stacks by collisions

More gets knocked off the longer the corridor (length), and the narrower the corridor, the higher the frequency of collisions

12.512.4For 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 Might help: Sweet model
12.6.112.5

For resistors in series: total potential difference is sum of potential differences across each resistor

As V = IR, the combined resistance of resistors in series = sum of individual resistances

Relating circuit to circuit diagram
12.6.212.6

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

Might help: A slope model for pd. Allow three ball-bearings to roll simultaneously down from the lip of a wide plastic funnel (held over a bowl). Each has its own route but the drop distance is the same each time.

Might help: Current model of group splitting up to go along three routes then rejoining again. Reduced resistance effect like using three delivery vans at the same time rather than one

12.7-

Some energy is dissipated as heat when a current flows through a conductor

Power P = VI

Energy H = V I t

Energy

Might help: Rope model
12.7.1-Practical applications of heating effect: heaters, toasters, etc., filament lamps, fusesWill all students be familiar with all of these examples?
12.8

Electric power:

P = V 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

Resource 3: Two models for teaching about electric circuits