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Resistance and Circuits Paper 4: Error Clinic
Resistance and Circuits Paper 4: Error Clinic
This paper targets the four most common slips: series voltage division, rated versus actual values, energy-cost units, and parallel simplification.
Direct answers Answers and explanations for all ten questions
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: DSE Physics Resistance and Circuits |
| Level | Paper 4 (error clinic) |
02 Questions (10 items)
- FoundationA 12 V battery is connected across a 3 ohm resistor. Find the current.
- FoundationTwo resistors of 10 ohms and 15 ohms are in parallel. Find the equivalent resistance.
- FoundationA 6 ohm resistor carries a current of 0.5 A. Find the power it dissipates.
- IntermediateA uniform 2 m resistance wire has a resistance of 8 ohms. Cut it to 0.5 m and find the new resistance.
- IntermediateA 12 ohm resistor is in series with two 6 ohm resistors in parallel, across a 12 V supply. Find the total resistance, the current, and the voltage across the parallel block.
- IntermediateAn 800 W appliance runs 3 hours a day for 30 days. Find the energy used and the cost at 1.1 dollars per kWh.
- ChallengeThree 12 ohm resistors in parallel are connected to a 12 V supply. Find the equivalent resistance and the total current.
- ChallengeA lamp is rated 12 V and 24 W. Find its resistance and the actual power when it is run at 9 V.
- ChallengeA motor takes in 1 500 J of electrical energy and delivers 1 050 J of mechanical energy. Find the efficiency and the energy lost as heat.
- Error redoError clinic: a student claims each of two 6 ohm resistors in series across 12 V gets the full 12 V. Correct the voltage, current and power.
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 4.0 A, from I equals V over R, that is 12 divided by 3. | Check the units first, then substitute into the current formula. |
| 2 | 5.999999999999999 ohms, since one over R equals one tenth plus one fifteenth. | A parallel combination is always smaller than its smallest member. |
| 3 | 1.5 W, from P equals I squared times R. | With current and resistance known, P equals I squared R skips the voltage step. |
| 4 | 2.0 ohms, because resistance falls in proportion to length. | With the same material and cross-section, a quarter of the length gives a quarter of the resistance. |
| 5 | The parallel block is 3.0 ohms, the total 15.0 ohms, the current 0.8 A and the block voltage 2.4000000000000004 V. | Simplify the parallel block first, then add the series part; voltage divides in proportion to resistance. |
| 6 | 72.00000000000001 kWh costing 79.20000000000002 dollars, from 0.8 kW times 3 hours times 30 days. | Convert watts to kilowatts first, or the energy comes out a thousand times too large. |
| 7 | 4.0 ohms and 3.0 A: identical branches divide the resistance by three, and the branch currents add up. | Each branch carries 1 A, so three branches give 3 A as a check. |
| 8 | The resistance is 6.0 ohms, and at 9 V the power is 13.5 W. | Treat the resistance as fixed: three quarters of the voltage leaves nine sixteenths of the power. |
| 9 | 70.0 per cent efficient, with 450 J lost as heat. | Output plus loss must equal input, which double-checks the efficiency. |
| 10 | Each takes only 6.0 V with 1.0 A, so 6.0 W each: voltage divides between equal resistors. | Giving the full supply voltage to every component is the classic series mistake. |
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.
Ask first whether the circuit is series or parallel, then whether the figures are rated or actual; those two questions remove most errors.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.