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S5 Physics: Circuits Practice Paper 4
S5 Physics: Circuits Practice Paper 4
Paper four starts with adding series resistances and reciprocals for parallel ones, then swaps voltage, current and power, then voltage division and branch currents, then a parallel-then-series network, energy units and an appliance rating, ending with the series-for-parallel mistake.
Quick answer 25 ohm, 4 ohm, 3 A and 54 W, 12 V and 6 W, 2 A with 4 V and 8 V, 6 ohm with 0.67 A and 0.33 A, 6 ohm and 4 V, 162 000 J which is 0.045 kWh, 6.8 A and 32 ohm, and 6 ohm with 2 A.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | 25 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S5 Physics: Circuits – Tutor Lesson Plan |
| Level | S5 |
02 Questions (10 items)
- FoundationTwo resistors of 10 ohm and 15 ohm are joined in series. Find the equivalent resistance.
- FoundationA 20 ohm and a 5 ohm resistor are connected in parallel. Find the equivalent resistance.
- FoundationAn 18 V supply drives a 6 ohm resistor. Find the current and the power.
- FoundationA current of 0.5 A flows through a 24 ohm resistor. Find the voltage across it and the power.
- IntermediateA 12 V supply is connected across 2 ohm and 4 ohm in series. Find the current and the voltage across each resistor.
- IntermediateA 6 V supply feeds 9 ohm and 18 ohm in parallel. Find the equivalent resistance, the total current and both branch currents.
- IntermediateA 3 ohm and 6 ohm parallel pair is in series with 4 ohm across 12 V. Find the total resistance, the total current and the voltage across the parallel section.
- ChallengeA 60 W lamp runs for 45 minutes. Find the energy used in joules and in kWh.
- ChallengeA 1 500 W kettle is rated at 220 V. Find the working current and the resistance of its element.
- Error redoTwo 12 ohm resistors in parallel are connected to 12 V. A student answers “24 ohm, so 0.5 A”. What is correct?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | The equivalent resistance is 25 ohm. | In series the resistances simply add and the same current flows through both. |
| 2 | The equivalent resistance is 4 ohm. | 1/R = 1/20 + 1/5 = 5/20, and a parallel value is always smaller than the smallest resistor. |
| 3 | Current 3 A and power 54 W. | First I = V/R gives 3 A, then P = I squared R or P = VI gives 54 W. |
| 4 | Voltage 12 V and power 6 W. | V = IR is 0.5 times 24, and P = VI is 12 times 0.5. |
| 5 | Current 2 A, with 4 V across the 2 ohm and 8 V across the 4 ohm. | Add to 6 ohm for the current, then use V = IR on each; the two voltages must add to 12 V. |
| 6 | Equivalent resistance 6 ohm, total current 1 A and branch currents of about 0.67 A and 0.33 A. | Both branches see the full 6 V, so use 6 over 9 and 6 over 18 directly. |
| 7 | Total resistance 6 ohm, total current 2 A and 4 V across the parallel section. | The pair simplifies to 2 ohm, plus 4 ohm makes 6 ohm, then multiply back for the section voltage. |
| 8 | 162 000 J, which is 0.045 kWh. | 45 minutes is 2 700 s, so E = Pt = 60 times 2 700; for kWh convert the time to hours first. |
| 9 | Current about 6.8 A and resistance about 32 ohm. | I = P/V is about 6.82 A, then R = V squared over P gives 32.3 ohm. |
| 10 | The equivalent is 6 ohm and the total current 2 A. | Parallel resistances add as reciprocals, so two equal ones halve; 24 ohm would be the series answer. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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