Energy, Power and Resistance | OCR A-Level Physics A (H556)
Energy, Power and Resistance
- 115 questions
- 8 subtopics
- Module 4: Electrons, waves and photons
- Paper 2 and Paper 3
Circuits from the component upwards: the symbols and diagrams, e.m.f.
and potential difference, Ohm's law and the components that disobey it, resistivity, and electrical power.
Sample questions from Energy, Power and Resistance
Answer each one closed book first, then open the answer.
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Circuit symbols and diagrams
Describe the circuit symbol for a light-dependent resistor (LDR).
Show the answer
A rectangular box enclosed in a circle with arrows pointing inward to represent incident light. -
Potential difference and e.m.f.
Define electromotive force (e.m.f.).
Show the answer
E.m.f. is the energy transferred per unit charge by a source (such as a cell or power supply) in driving charge around a complete circuit. -
Energy transfer in circuits
When we say a component has a p.d. across it, in which direction is energy being transferred?
Show the answer
Energy is transferred from the charge carriers to the component. -
Ohm's law and I-V characteristics
Calculate the resistance when potential difference = 2 V, current = 4.9 A.
Show the answer
Resistance = 2 ÷ 4.9 = 0.408 Ω. -
Filament lamps, diodes, thermistors and LDRs
What is a thermistor?
Show the answer
A component whose resistance changes significantly with temperature. -
Resistivity and how it is measured
What is the SI unit of resistivity?
Show the answer
The ohm-metre (Ω m). -
How resistivity varies with temperature
Explain why the resistivity of a semiconductor decreases when it is heated.
Show the answer
Increasing temperature provides thermal energy that excites more electrons from the valence band to the conduction band, increasing the number of charge carriers available for conduction, which reduces resistivity. -
Electrical power and the kilowatt-hour
State the equation for energy transferred in an electrical circuit in terms of current, potential difference, and time.
Show the answer
W = VIt, where W is energy in joules, V is potential difference in volts, I is current in amperes, and t is time in seconds.
The 8 subtopics
One subtopic is one session. Work down the list.
| Subtopic | What it covers | Questions |
|---|---|---|
| Circuit symbols and diagrams | Recall questions on the standard symbols and on reading and drawing a circuit diagram. | 19 |
| Potential difference and e.m.f. | Recall questions on the volt, and on what distinguishes the e.m.f. of a source from a potential difference across a component. | 9 |
| Energy transfer in circuits | Recall questions on W = VQ and W = EQ, and on the energy gained by a charge accelerated through a potential difference. | 8 |
| Ohm's law and I-V characteristics | Recall questions on resistance and its unit, Ohm's law, R = V/I calculations, ohmic and non-ohmic components, the I-V characteristic of a resistor, and investigating I-V characteristics with a potential divider and spreadsheet. | 15 |
| Filament lamps, diodes, thermistors and LDRs | Recall questions on why filament lamp resistance rises with current, NTC thermistors and their non-linear I-V characteristic, diodes and LEDs and their I-V characteristics, and how LDR resistance changes with light intensity. | 14 |
| Resistivity and how it is measured | Recall questions on resistivity as a material property, R = ρL/A, its unit and calculations, and measuring the resistivity of a wire: instruments, cross-sectional area from diameter and repeated diameter readings. | 11 |
| How resistivity varies with temperature | Recall questions on how the resistivity of metals and semiconductors changes with temperature and why, negative temperature coefficients, and NTC thermistors as temperature sensors. | 12 |
| Electrical power and the kilowatt-hour | Recall questions on the three expressions for power, energy transferred as VIt, and calculating a domestic bill. | 27 |
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.