6 equations. Each page has 10 real-life ramped questions with full FIFA solutions. Every equation is given on the equation sheet in the exam.
Key: C+S = Combined and Separate | S only = Separate Physics only | HT = Higher tier only
- Charge flow: Q = It (C+S)
- Potential difference: V = IR (C+S)
- Power: P = VI (C+S)
- Power: P = I²R (C+S)
- Energy transferred: E = Pt (C+S)
- Energy transferred: E = QV (C+S)
Key definitions
Write your answer on paper first, then tap Show answer. Learn the key words – definition questions are quick marks in the exam.
1. What is electric current? (C+S)
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The rate of flow of electrical charge. Unit: ampere (A). 1 A = 1 coulomb per second.
2. What is potential difference? (C+S)
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The energy transferred per unit charge passing between two points. Unit: volt (V). 1 V = 1 joule per coulomb.
3. What is resistance? (C+S)
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The opposition to the flow of current in a component. Unit: ohm (Ω). The greater the resistance, the smaller the current for a given potential difference.
4. What is an ohmic conductor? (C+S)
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A conductor where the current is directly proportional to the potential difference, at constant temperature – so its resistance stays the same.
5. State the rules for current, potential difference and resistance in a series circuit. (C+S)
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The current is the same through each component. The total p.d. of the supply is shared between the components. The total resistance is the sum of the individual resistances (Rtotal = R1 + R2).
6. State the rules for current, potential difference and resistance in a parallel circuit. (C+S)
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The p.d. across each branch is the same. The total current is the sum of the currents through the separate branches. The total resistance is less than the resistance of the smallest individual resistor.
7. How does the resistance of a thermistor and an LDR change? (C+S)
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Thermistor: resistance decreases as temperature increases. LDR: resistance decreases as light intensity increases.
8. Describe how current flows through a diode and a filament lamp. (C+S)
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Diode: current flows in one direction only – it has a very high resistance in the reverse direction. Filament lamp: as the current increases, the filament gets hotter and its resistance increases.
9. What is the difference between direct current and alternating current? (C+S)
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Direct current (d.c.) flows in one direction only (e.g. from a cell or battery). Alternating current (a.c.) repeatedly changes direction.
10. State the frequency and potential difference of the UK mains supply. (C+S)
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The UK mains is an a.c. supply with a frequency of 50 Hz and a potential difference of about 230 V.
11. Give the colour and job of the live, neutral and earth wires. (C+S)
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Live (brown): carries the alternating p.d. from the supply (about 230 V). Neutral (blue): completes the circuit; at or close to 0 V. Earth (green and yellow): a safety wire that stops the appliance casing becoming live; it only carries current if there is a fault.
12. What is the National Grid, and why does it transmit electricity at a high potential difference? (C+S)
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A system of cables and transformers linking power stations to consumers. Step-up transformers increase the p.d., which reduces the current in the cables. A smaller current means less energy is wasted heating the cables, so transmission is more efficient. Step-down transformers then reduce the p.d. to a safer level for homes.
