Electric Circuits | Edexcel A-Level Physics (9PH0)
Electric Circuits
- 148 questions
- 14 subtopics
- Paper 1: Advanced Physics I
- Paper 1 and Paper 3
Paper 1 content, examined again synoptically on Paper 3.
Covers current, potential difference and resistance from their definitions, Kirchhoff's two laws and combining resistances, the characteristics of lamps, diodes, thermistors and light dependent resistors, resistivity and drift velocity, potential dividers, and internal resistance.
Sample questions from Electric Circuits
Answer each one closed book first, then open the answer.
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Current, charge and potential difference
Which charged particles carry the current in a metal wire?
Show the answer
The free (delocalised) conduction electrons. -
Resistance, Ohm's law and ohmic behaviour
State the equation for the power dissipated in a component in terms of potential difference and current:
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P = VI, where P is the power in watts. -
Kirchhoff's laws: the current and potential difference rules
Which conservation law explains how the potential differences are shared around a circuit loop?
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Conservation of energy, since each coulomb must deliver all the energy it gained from the source by the time it returns to it. -
Combining resistances in series and parallel
Two identical resistors of resistance R are connected in parallel. What is their combined resistance?
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The combined resistance is R/2. -
I-V characteristics of conductors, lamps and diodes
Why does the characteristic curve of a filament lamp bend over as the current increases?
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The larger current heats the filament, and the resistance of the metal rises with temperature, so equal increases in potential difference produce progressively smaller increases in current. -
Thermistors, light dependent resistors and resistance change
Why is the characteristic of a filament lamp symmetrical about the origin while that of a diode is not?
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A filament behaves the same way whichever direction the current flows, whereas a diode has a junction that conducts easily in one direction only. -
Charge carriers, drift velocity and I = nqvA
Why does a lamp light almost instantly even though the drift velocity of the electrons is only about a millimetre per second?
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The electric field is established along the whole circuit at close to the speed of light, so every electron in the wire, including those already inside the filament, begins to drift at essentially the same moment. -
The potential divider equation and the loading effect
A 12 V supply is connected across a 3.0 kΩ resistor in series with a 1.0 kΩ resistor. What is the potential difference across the 1.0 kΩ resistor?
Show the answer
V = 12 × 1.0/(3.0 + 1.0) = 3.0 V.
The 14 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Current, charge and potential difference | Recall questions on current as rate of flow of charge, the definitions of the coulomb and the volt, and which particles carry the current in a metal. | 10 |
| Resistance, Ohm's law and ohmic behaviour | Recall questions on the definition of resistance and the ohm, the condition attached to Ohm's law, and why R = V/I is not the same statement. | 9 |
| Electrical power and energy | Recall questions on the three power equations and where they come from, which resistor dissipates more in series and in parallel, and why transmission uses high voltage. | 8 |
| Kirchhoff's laws: the current and potential difference rules | Recall questions on the junction and loop rules, the conservation laws behind them, and how current and potential difference are shared in series and parallel. | 9 |
| Combining resistances in series and parallel | Recall questions on the series and parallel equations, why a parallel combination is smaller than its smallest member, and what adding another branch does. | 8 |
| Circuit calculations, meters and component failure | Recall questions on splitting potential difference and current between resistors, why an ammeter goes in series and a voltmeter in parallel, and what happens when a lamp fails. | 8 |
| I-V characteristics of conductors, lamps and diodes | Recall questions on the shapes of the metallic, filament lamp and diode characteristics, the threshold potential difference, and why a lamp is not ohmic. | 10 |
| Thermistors, light dependent resistors and resistance change | Recall questions on why a metal's resistance rises with temperature while a thermistor's falls, what NTC means, and why an LDR's resistance drops in bright light. | 13 |
| Resistivity and determining it experimentally | Recall questions on R = ρl/A, the unit of resistivity, and the wire experiment, including why the diameter is measured repeatedly and the current kept low. | 13 |
| Charge carriers, drift velocity and I = nqvA | Recall questions on the meaning of each symbol in I = nqvA, number density and drift velocity, and why a lamp lights instantly although electrons drift slowly. | 11 |
| The potential divider equation and the loading effect | Recall questions on how potential falls along a uniform wire, the divider equation and its derivation, and why the output drops when a load is connected. | 12 |
| Sensing circuits with thermistors and light dependent resistors | Recall questions on thermistor and LDR dividers, which way round to take the output, choosing the fixed resistor, and switching a heater from a temperature sensor. | 12 |
| Electromotive force, internal resistance and lost volts | Recall questions on the definition of e.m.f., what internal resistance is, the lost volts, and when terminal potential difference equals e.m.f. | 12 |
| Measuring e.m.f. and internal resistance, and cells in combination | Recall questions on the experiment, the graph plotted and what its gradient and intercept give, the largest current a cell can deliver, and cells in series and parallel. | 13 |
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
Edexcel A-Level Physics Active Recall Guide
Every topic, not just this one. 1,616 questions with their answers.