Electricity
Electricity is the flow of electric charge around a circuit, driven by a potential difference (voltage) and opposed by resistance. GCSE physics covers series and parallel circuits, current-voltage graphs for components such as resistors, filament lamps, diodes and thermistors, and calculating charge, power and energy in circuits and the UK mains supply.
Method
- Identify whether the circuit is series or parallel, since current and potential difference behave differently in each.
- Recall the key rules: in series, current is the same everywhere and potential differences add up; in parallel, potential difference is the same across each branch and currents add up.
- Choose the correct equation for the quantity you need, such as charge = current x time, potential difference = current x resistance, or power = current x potential difference.
- Substitute the given values, keeping units in amps, volts, ohms, seconds and watts.
- Carry out the calculation step by step, rearranging the equation first if needed.
- Check your answer is sensible, for example household currents are usually a few amps, not thousands.
Worked example
A hairdryer is connected to the 230 V UK mains supply and draws a current of 6.0 A. Calculate the power of the hairdryer.
- Write down the equation linking power, potential difference and current: power = potential difference x current.
- Substitute the values: power = 230 x 6.0.
- Calculate: 230 x 6.0 = 1380.
- State the final answer with the correct unit: power = 1380 W (1.38 kW).
Practice questions
Try each question, then tap to reveal the answer.
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
A lamp is connected to a 12 V supply and a current of 0.50 A flows through it for 4.0 minutes. Calculate the charge that flows through the lamp. Use: charge = current x time.
A student carries out the required practical to investigate the I-V characteristics of a filament lamp, using a circuit containing a power supply, an ammeter, a voltmeter and the lamp. (a) State the correct positions of the ammeter and the voltmeter in the circuit. (2 marks) (b) Explain why the current through the filament lamp increases less rapidly as the potential difference increases. (3 marks)
A thermistor is connected into a circuit that controls a greenhouse heater. (a) State how the resistance of a thermistor changes as its temperature decreases. (1 mark) (b) Explain how this change in resistance can be used to switch the heater on automatically when the greenhouse gets cold. (3 marks)
Free printable worksheet
Want more practice on paper? Download the electricity worksheet pack - 18 pages of exam-style questions with a full mark scheme. No sign-up, no email wall - just the PDF, free for personal and classroom use.
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