Edexcel International A Level Physics
Edexcel International A Level Physics Electric Circuits Exam Questions
Free Edexcel International A Level Physics exam questions for Electric Circuits, with a mark scheme for every pack. Covers current, charge, potential difference, resistance, resistivity, I = nqvA, I-V graphs, potential dividers and e.m.f. and internal resistance.
Electric Circuits exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About Edexcel International A Level Physics Electric Circuits
Electric circuits is part of Unit 2: Waves and Electricity in Edexcel International A Level Physics. It covers electrical quantities such as charge, current, potential difference, resistance and power, and the microscopic model of current using I = nqvA. You analyse series and parallel circuits, I-V characteristics of components, potential dividers with thermistors and LDRs, and e.m.f. and internal resistance. These ideas are needed again for capacitors in Unit 4. Examiners commonly ask you to explain resistance changes in terms of charge carrier density and lattice vibrations, and to determine e.m.f. and internal resistance from a graph.
What you need to know
- Current and charge I = ΔQ/Δt. Current in a conductor I = nqvA, where n is the number density of charge carriers and v is the drift velocity.
- Potential difference and power V = W/Q, P = VI = I^2R = V^2/R and W = VIt.
- Resistance R = V/I and R = ρl/A. Know I-V graphs for an ohmic conductor, a filament lamp, a diode and a thermistor.
- Series and parallel Series: R = R1 + R2 + R3; parallel: 1/R = 1/R1 + 1/R2 + 1/R3. Current is conserved at junctions and energy is conserved around loops.
- Potential dividers Vout = R2Vin/(R1 + R2). Used with a thermistor or LDR to produce a sensor whose output depends on temperature or light.
- E.m.f. and internal resistance ε = I(R + r), V = ε - Ir. A graph of V against I has gradient -r and y-intercept ε.
Common mistakes in Electric Circuits
- Explaining a thermistor's falling resistance only through fewer collisions. The main reason is that more charge carriers are released, so n increases.
- Treating resistance as the gradient of an I-V graph rather than V/I.
- Forgetting that the parallel combination is smaller than the smallest resistor.
- Ignoring internal resistance, so the terminal p.d. is wrongly taken as the e.m.f.
- Using diameter as radius in resistivity calculations.
Try three Electric Circuits exam-style questions
1. A current of 0.50 A flows for 2.0 minutes. Calculate the charge passing and the number of electrons this represents. (3 marks)
Show the mark scheme answer
Q = It = 0.50 × 120 = 60 C; number of electrons = 60/1.60 × 10^-19; = 3.75 × 10^20.
2. A 12 V supply is connected to a 24 Ω resistor. Calculate the power dissipated. (1 mark)
Show the mark scheme answer
P = V^2/R = 144/24 = 6.0 W.
3. Explain why the resistance of a filament lamp increases as the current through it increases. (3 marks)
Show the mark scheme answer
Increasing current increases the temperature of the filament; lattice ions vibrate with greater amplitude so charge carriers collide more often (drift velocity reduced for a given p.d.); so resistance increases.
Electric Circuits FAQs
What does Edexcel International A Level Physics Electric circuits cover?
It covers charge, current, potential difference, power, resistance and resistivity, I = nqvA, I-V characteristics, series and parallel circuits, potential dividers and e.m.f. and internal resistance.
Which unit is Electric circuits examined in?
It is examined in Unit 2: Waves and Electricity, and circuit experiments are common in the practical skills papers.
How do I find e.m.f. and internal resistance experimentally?
Vary an external resistance, record terminal p.d. and current, and plot V against I; the y-intercept is the e.m.f. and the gradient is minus the internal resistance.
