Edexcel A Level Physics
Edexcel A Level Physics Topic 3: Electric Circuits Exam Questions
Free Edexcel A Level Physics exam questions for Topic 3: Electric Circuits, with a mark scheme for every pack. Covers charge, current, potential difference, resistance, resistivity, I-V graphs, series and parallel circuits, potential dividers and internal resistance.
Topic 3: Electric Circuits exam questions
2 question packs 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 A Level Physics Topic 3: Electric Circuits
Topic 3: Electric Circuits in Edexcel A Level Physics covers electrical quantities and components, then circuits and internal resistance. You explain current in terms of charge carriers using I = nqvA, apply resistivity, analyse I-V characteristics, and use series and parallel rules, potential dividers and e.m.f. with internal resistance. Two core practicals belong here: determining the electrical resistivity of a material and the e.m.f. and internal resistance of a cell. The topic appears in Paper 1: Advanced Physics I and supports later work on capacitors. Examiners like explanations using n and v for thermistors and filament lamps.
What you need to know
- Charge and current I = ΔQ/Δt and I = nqvA, where n is the number density of charge carriers and v the drift velocity. Current is conserved at junctions.
- Potential difference and power V = W/Q; P = VI = I^2R = V^2/R; W = VIt.
- Resistance and resistivity R = V/I and R = ρl/A. Ohm's law applies when R is constant. Know I-V graphs for an ohmic conductor, filament lamp and diode.
- Series and parallel Series: R = R1 + R2 + R3; parallel: 1/R = 1/R1 + 1/R2 + 1/R3. Conservation of charge and energy underpin these rules.
- Potential dividers Vout = R2Vin/(R1 + R2). Thermistors and LDRs in potential dividers make sensing circuits; the resistance of an NTC thermistor falls as temperature rises because n increases.
- E.m.f. and internal resistance ε = I(R + r) and V = ε - Ir. A graph of terminal p.d. against current has gradient -r and intercept ε.
Common mistakes in Topic 3: Electric Circuits
- Explaining a thermistor's falling resistance only in terms of fewer collisions. Its resistance falls mainly because more charge carriers are released (n increases).
- Using the gradient of an I-V graph as resistance. Resistance is V/I at each point.
- Ignoring internal resistance when the cell's terminal p.d. is less than its e.m.f.
- Getting potential divider changes backwards. If R2 increases, the share of the supply p.d. across R2 increases.
- Forgetting to convert diameter to radius and mm to m in resistivity calculations.
Try three Topic 3: Electric Circuits exam-style questions
1. A cell of e.m.f. 1.5 V and internal resistance 0.80 Ω is connected to a 4.2 Ω resistor. Calculate the current and the terminal potential difference. (3 marks)
Show the mark scheme answer
I = ε/(R + r) = 1.5/5.0 = 0.30 A; V = IR = 0.30 × 4.2; V = 1.26 V.
2. A 9.0 V supply is connected across a 2.0 kΩ resistor in series with a thermistor of resistance 4.0 kΩ. Calculate the p.d. across the thermistor and state how it changes when the thermistor is warmed. (3 marks)
Show the mark scheme answer
V = 9.0 × 4.0/(2.0 + 4.0) = 6.0 V; thermistor resistance decreases as it warms; so p.d. across it decreases.
3. Describe how to determine the resistivity of a metal wire. (4 marks)
Show the mark scheme answer
Measure diameter at several points with a micrometer and find the mean to calculate A; measure R for several lengths l using an ammeter and voltmeter (or ohmmeter); keep current low to avoid heating; plot R against l and ρ = gradient × A.
Topic 3: Electric Circuits FAQs
What does Edexcel A Level Physics Topic 3: Electric Circuits cover?
It covers current, charge carriers and I = nqvA, potential difference, power, resistance and resistivity, I-V characteristics, series and parallel circuits, potential dividers and internal resistance.
Which paper is Topic 3: Electric Circuits examined in?
It is assessed in Paper 1: Advanced Physics I, and like every topic it can also appear in Paper 3: General and Practical Principles in Physics.
Which core practicals are in Electric Circuits?
Determining the electrical resistivity of a material, and determining the e.m.f. and internal resistance of an electrical cell.
