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
Type your answer and press Check to be marked straight away, or reveal the answer and mark yourself.
Q1In a series circuit, the current through one lamp is 0.30 A. State the current through a second lamp in the same circuit.Show answer
Answer: 0.30 A (current is the same everywhere in a series circuit)
Q2State the UK mains supply frequency and typical potential difference.Show answer
Answer: 50 Hz and 230 V
Q3A current of 2.0 A flows through a resistor for 30 s. Calculate the charge that flows. Use Q = I x t.Show answer
Answer: 60 C (2.0 x 30)
Q4Two resistors are connected in parallel across a 12 V battery. State the potential difference across each resistor.Show answer
Answer: 12 V (potential difference is the same across each parallel branch, equal to the battery p.d.)
Q5A resistor of resistance 15 ohm is connected to a 6.0 V supply. Calculate the current flowing through it. Use V = I x R.Show answer
Answer: 0.40 A (6.0/15)
Q6A component has a current of 5.0 A and a resistance of 8.0 ohm. Calculate the power dissipated using P = I^2 x R.Show answer
Answer: 200 W (5.0^2 x 8.0 = 25 x 8.0)
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.
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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)
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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)
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See real GCSE Science past-paper questions, with official mark schemes →
Free printable worksheet
Want more practice on paper? Download the electricity worksheet pack - 18 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 2 of GCSE Physics Workbook, the whole course as one free printable PDF.
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