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Resistance and Circuits Paper 1: Basics
Resistance and Circuits Paper 1: Basics
Starting from V = IR: single resistors, series addition, parallel reciprocals, then power and electricity cost, all from one main formula.
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 1 (basics) |
02 Questions (10 items)
- FoundationA current of 2 A passes through a 6 ohm resistor. Find the voltage across it.
- FoundationA resistor across a 9 V supply carries 0.5 A. Find its resistance.
- FoundationA 4 ohm and a 6 ohm resistor are joined in series. Find the total resistance.
- IntermediateA 6 ohm and a 3 ohm resistor are joined in parallel. Find the total resistance.
- IntermediateA 12 V supply drives 4 ohm and 2 ohm resistors in series. Find the current and the voltage across the 4 ohm resistor.
- IntermediateA current of 0.5 A flows through a 20 ohm resistor. Find the power dissipated.
- ChallengeResistors of 6, 3 and 2 ohms are joined in parallel. Find the total resistance.
- ChallengeTwo resistors in parallel give 4 ohms and one of them is 12 ohms. Find the other.
- ChallengeA 60 W lamp runs for 5 hours. Find the energy used in kWh and the cost at 1.2 dollars per kWh.
- Error redoError clinic: a student writes 12 ohms for two 6 ohm resistors in parallel. Find the correct total and the mistake.
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 12 V, from V = IR, that is 2 times 6. | Amperes multiplied by ohms give volts, so the unit is V. |
| 2 | 18.0 ohms, from R = V divided by I. | Resistance is voltage divided by current, not multiplied. |
| 3 | 10 ohms: resistances in series simply add. | In series the current is the same everywhere while the voltage divides in proportion to resistance. |
| 4 | 2.0 ohms: one over R is one over 6 plus one over 3, which is one half. | Parallel resistances add as reciprocals, and the answer must be smaller than the smallest branch. |
| 5 | The current is 2.0 A and the voltage across 4 ohms is 8.0 V: the total is 6 ohms, so 12 divided by 6 gives the current. | Find the total resistance first, then the current, and only then the voltage across each part. |
| 6 | 5.0 W, from P = I squared times R. | All three power formulas hold in a pure resistance circuit; P = I squared R is quickest here. |
| 7 | 1.0 ohm: the reciprocals add to one, so the resistance is one ohm. | More parallel branches always lower the total, so the answer must be below 2 ohms. |
| 8 | 5.999999999999999 ohms: one over the unknown is one quarter minus one twelfth. | Work with reciprocals when reversing a parallel combination; subtracting the values themselves gives a negative result. |
| 9 | 0.3 kWh costing 0.36 dollars: 60 W is 0.06 kW and 0.06 times 5 is 0.3. | Convert watts to kilowatts, multiply by hours, and only then apply the tariff. |
| 10 | The correct total is 3.0 ohms; the student added them as if they were in series. | A parallel total is always below the smallest branch, and only series resistances add directly. |
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.
List two of the three quantities before choosing a formula, then substitute, keeping units with the numbers.Tutor Registration →
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