Electricity in the Home *suitable for home teaching*

A Year Ten module from the Salters double award science course. Models are used to illustrate conservation of current in a series circuit leading to studies of voltage, current and resistance and the resistance law. Devices which have different resistance in response to conditions, such as LDRs and thermistors are investigated. Students then explore the different switching arrangements possible with series and parallel circuits. The additivity of current in the common branches of branched circuits is established.

Relationships between voltage, current and amount of energy transferred are established, leading to an explanation of why domestic appliances are marked in watts rather than amps.
Study of the heating effect of current leads to ideas about fuses and other safety devices. A model ring main circuit can be constructed.

A study of batteries leads to revision of the reactivity series. The ideas developed in the module are revised through an exercise to design the electrical layout for a touring caravan.

Section 1: What is electricity?
Applications and dangers of electric sparks are reviewed and the Van de Graaf generator may be demonstrated. The idea of current as movement of charge is developed, A simple voltaic cell may be modelled as a way of separating charge to produce a current.

Section 2: How much current?
Experiments and analogies are used to confirm that current is conserved round a series circuit. The net transfer of charge in some circuits is calculated. Voltage and current relationships are explored to introduce the concept of resistance. Some devices with varying resistance are tested. Components are connected both in series and in parallel to show features of different circuit types.

Section 3: Voltage – energy for the nation?
The effect of applying different voltages is observed. Resistance is defined by the relationship V = I x R. Work with immersion heaters leads to a definition of voltage as the measure of energy supplied to each unit of charge. Voltage relationships in different parts of both series and parallel circuits are tested.

Section 4: Keeping it safe at home
Potential dangers of the heating effect of current are pointed out. Circuits including “weak links” are tested. The action of earth leads, fuses and circuit breakers are studied. Students make a model ring main and consider how domestic wiring is arranged.

Section 5: Portable power
Simple cells are modelled and compared with a ‘dry’ cell. The difference between simple and rechargeable cells is explored. Ideas from the unit are drawn together as students design the electrical layout for a touring caravan, and calculate current loadings and running costs.