Electrical Circuits | OCR A-Level Physics A (H556)
Electrical Circuits
- 43 questions
- 3 subtopics
- Module 4: Electrons, waves and photons
- Paper 2 and Paper 3
Analysing complete circuits: Kirchhoff's two laws, why a real source cannot deliver its full e.m.f., and the potential divider..
It covers kirchhoff's laws and combining resistances, e.m.f., internal resistance and lost volts and potential dividers.
Sample questions from Electrical Circuits
Answer each one closed book first, then open the answer.
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Kirchhoff's laws and combining resistances
Explain why the total resistance of resistors in series equals the sum of the individual resistances.
Show the answer
In series, the same current flows through each resistor, and the total potential difference is the sum of the p.d.s across each. Applying V = IR to each resistor and summing gives R_total = R₁ + R₂ + … -
Kirchhoff's laws and combining resistances
How is the total current distributed in a parallel circuit?
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The total current is shared between the branches. -
E.m.f., internal resistance and lost volts
State the equation relating e.m.f. to current, external resistance and internal resistance.
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ε = I(R + r), where ε is e.m.f., I is current, R is external resistance and r is internal resistance. -
E.m.f., internal resistance and lost volts
Where should the voltmeter be connected when measuring terminal p.d. to determine internal resistance?
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Across the terminals of the cell. -
Potential dividers
How does the resistance of a light-dependent resistor (LDR) change with light intensity?
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The resistance decreases as the light intensity incident upon it increases. -
Potential dividers
How should a potential divider be set up to investigate how output voltage varies with a physical quantity such as temperature or light intensity?
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Set up a potential divider with a fixed resistor and a sensor (e.g. thermistor or LDR).
The 3 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Kirchhoff's laws and combining resistances | Recall questions on Kirchhoff's first and second laws and the conservation principles behind them, resistors in series and parallel with calculations, and how current and potential difference are shared in series and parallel circuits. | 13 |
| E.m.f., internal resistance and lost volts | Recall questions on internal resistance, terminal potential difference, and how both are determined experimentally. | 15 |
| Potential dividers | Recall questions on potential dividers and potentiometers, the potential divider equation and calculations, sensing circuits with LDRs and thermistors, and investigating how output voltage varies with light or temperature. | 15 |
How the guide is worked
Answering a question from memory stores it far better than reading the answer again. The guide runs that as a fixed procedure on one subtopic at a time, about twenty minutes a session.
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Step 1 · Closed book
Cover the answers. Work through one subtopic and write down what you can. Leave blanks where you have nothing.
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Step 2 · Open book
Go back to the top. Read each printed answer and write it out in full, including the ones you had right.
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Step 3 · Closed book again
Same questions, same order, from memory. The gap between pass one and pass three is the session result.
Read the full method, the return schedule and the research behind it.
Nearby topics
OCR A-Level Physics A Active Recall Guide
Every topic, not just this one. 1,862 questions with their answers.