Electricity
Circuit diagrams, meters, series and parallel circuits, power ratings and the cost of electricity.
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Before you begin
A circuit is a complete path for electric current. This topic draws and builds circuits, measures current, voltage and resistance, compares series and parallel circuits, and uses power ratings to work out the cost of electricity.
Be comfortable with: multiplying and dividing decimals, and converting watts to kilowatts and minutes to hours.
Learning goals
- Draw and interpret circuit diagrams and components
- Set up physical circuits safely using the specified components
- Series and parallel arrangements
- Using a multimeter
- Current in series
- Potential difference in series
- Resistance in series
- Current in parallel
- Potential difference in parallel
- Resistance in parallel
- Household parallel wiring
- Appliance ratings
- Electrical power
- Cost in kilowatt-hours
- Reading an electricity bill
- Reducing electrical-energy wastage
Syllabus statements covered
- draw and interpret circuit diagrams, and set up circuits, with power sources (cell or battery), switches, lamps, resistors (fixed and variable), bells, fuses, ammeters and voltmeters
- identify series and parallel arrangements of circuit components
- use a multimeter to measure current, voltage and resistance
- state that the current is the same at every point in a series circuit
- state that the voltage across the power source is equal to the sum of voltages across the other components in a series circuit
- state that the effective resistance increases when the number of resistors connected in series increases
- state that the current through the power source is the sum of the currents in the separate branches of a parallel circuit
- state that the voltage is the same across the separate branches of a parallel circuit
- state that the effective resistance decreases when the number of resistors connected in parallel increases
- explain the advantages of connecting household appliances in parallel
- identify voltage rating and power rating found on a label of an electrical appliance
- recall and apply the relationship power = current × voltage to solve problems
- calculate the cost of using electrical appliances where the energy unit is the kWh
- identify electricity usage found on an electricity bill
- state some ways to reduce electrical energy wastage in daily lives (e.g. use energy-efficient appliances)
Lessons
Work through them in order.
- Circuit diagrams and arrangementsRead circuit diagrams, build simple circuits with low-voltage cells, and distinguish series from parallel connections.
- Measuring current, potential difference and resistanceUse a meter to measure current in series, and potential difference and resistance across a component.
- Series circuitsExplain why current is the same all round a series circuit and potential differences add up to the supply.
- Parallel circuits and household wiringAdd branch currents at junctions and explain why every parallel branch has the full supply potential difference.
- Appliance ratings and electrical powerRead an appliance's voltage and power ratings, and calculate power from current and potential difference.
- Electrical energy, bills and costCalculate energy use in kilowatt-hours and its cost from meter readings, and find ways to save energy.
Practise and check
Or choose
Topic reference
Quick reference
| Quantity | Formula | Unit |
|---|---|---|
| power | P = IV | watt (W) |
| energy used | power (kW) × time (h) | kilowatt-hour (kWh) |
| cost | energy (kWh) × price per kWh | dollars |
| Circuit | Current | Voltage |
|---|---|---|
| series | the same at every point | shared between components; adds to supply |
| parallel | branch currents add up to supply current | the full supply voltage across each branch |
Core knowledge to remember
- An ammeter is connected in series; a voltmeter is connected across a component.
- Resistance is measured with the component disconnected from the supply.
- Adding a resistor in series increases the total resistance; adding a branch in parallel decreases it.
- Household appliances are wired in parallel, so each gets the full supply voltage and works independently.
- A kilowatt is a unit of power; a kilowatt-hour is a unit of energy.
Common mistakes
- Connecting an ammeter across a component, or a voltmeter in series.
- Saying current is used up as it passes through components in series.
- Assuming current splits equally between parallel branches.
- Using watts or minutes in the kilowatt-hour formula.