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S4 Physics: Circuits in Series and Parallel – Foundation (10 Questions)
S4 Physics: Circuits in Series and Parallel – Foundation (10 Questions)
This paper builds the basics: adding resistances in series, adding reciprocals in parallel, voltage division in series against current division in parallel, the three power formulas, lamp ratings, internal resistance and terminal voltage, the bounds on series and parallel totals, and a final item on three common series and parallel misconceptions.
Quick answer The 9 V series loop gives 1 A with 6 V and 3 V; the 12 V parallel pair gives 2 ohm and 6 A, split 2 A and 4 A; three 4 ohm resistors take 4 W each; 10 ohm in parallel with 2 ohm gives 7 ohm and 2 A; the 24 V network runs 2 A with 8 V across the pair; a 4.5 V reading means 1.5 A and 13.5 V; the 12 V 24 W lamp is 6 ohm and takes 6 W at 6 V; an internal resistance of 0.5 ohm gives 91.7 percent efficiency; 2, 3 and 6 ohm give 11 ohm in series and 1 ohm in parallel; and three misconceptions are corrected.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 20 minutes |
| Difficulty mix | Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1 |
| Chapter | Chapter: S4 Physics | Circuits in Series and Parallel: Resistance, Current, Voltage and Power |
| Level | S4 |
02 Questions (10 items)
- FoundationTwo resistors of 6 ohm and 3 ohm are joined in series across a 9 V battery. Find the total resistance, the current and the voltage across each resistor.
- FoundationA 6 ohm and a 3 ohm resistor are connected in parallel to a 12 V supply. Find the equivalent resistance, the total current and the current in each branch.
- FoundationThree identical 4 ohm resistors are in series across a 12 V supply. Find the current and the power dissipated in each resistor.
- FoundationTwo 10 ohm resistors in parallel are joined in series with a 2 ohm resistor across a 14 V supply. Find the total resistance, the total current and the voltage across the parallel pair.
- IntermediateA 12 ohm and a 6 ohm resistor in parallel are in series with 8 ohm across 24 V. Find the total current, the voltage across the parallel pair and the current in each branch.
- IntermediateA 6 ohm and a 3 ohm resistor are in series and a voltmeter across the 3 ohm reads 4.5 V. Find the current and the supply voltage.
- IntermediateA lamp is marked 12 V, 24 W. Find its resistance and normal current, and the power when it is connected to 6 V assuming the resistance stays the same.
- ChallengeA battery of emf 12 V and internal resistance 0.5 ohm is connected to an external 5.5 ohm resistor. Find the current, terminal voltage, external power, internal loss and efficiency.
- ChallengeThree resistors of 2 ohm, 3 ohm and 6 ohm. Find the total resistance with all in series and all in parallel, and the ratio of the two.
- Error redoThree students write that current is used up by each resistor in series, that adding a resistor in parallel raises the total resistance, and that the larger resistor carries more current in parallel. Correct each statement.
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | The total resistance is 9 ohm, the current is 1 A, and the voltages are 6 V across the 6 ohm and 3 V across the 3 ohm. | The current is the same everywhere in a series circuit, so the voltages divide in the ratio of the resistances, 2 to 1 here. |
| 2 | The equivalent resistance is 2 ohm, the total current is 6 A, with 2 A through the 6 ohm and 4 A through the 3 ohm. | Branches in parallel share the same voltage, so the currents are inversely proportional to the resistances and the 3 ohm branch carries twice the current. |
| 3 | The total resistance is 12 ohm and the current is 1 A, so each resistor dissipates 4 W and the circuit takes 12 W in total. | The current is common in series, so power is the square of the current times each resistance, and three equal resistors share the total equally. |
| 4 | The parallel pair is 5 ohm, the total resistance is 7 ohm, the current is 2 A and the parallel pair carries 10 V. | Reduce the parallel pair first and then add the series part; the series current is common, so the parallel voltage is 2 A times 5 ohm. |
| 5 | The parallel pair is 4 ohm, the total resistance 12 ohm, the current 2 A and the parallel voltage 8 V, giving 0.667 A and 1.333 A in the branches. | The total current splits at the junction in inverse proportion to resistance, and the two branch currents add back to 2 A. |
| 6 | The current is 1.5 A and the supply voltage is 13.5 V. | The voltmeter reads the drop across the 3 ohm only, so find the current first and then multiply by the total resistance. |
| 7 | The normal current is 2 A and the resistance 6 ohm; at 6 V the power is 6 W, a quarter of the rating. | With a fixed resistance the power goes as the square of the voltage, so halving the voltage cuts the power to a quarter. |
| 8 | The current is 2 A, the terminal voltage 11 V, the external power 22 W and the internal loss 2 W, an efficiency of about 91.7 percent. | The internal resistance is in series with the load, so the efficiency is the external power divided by the total power. |
| 9 | In series the total is 11 ohm and in parallel 1 ohm, a ratio of 11. | A parallel combination is always smaller than its smallest member, while a series combination is always larger than its largest. |
| 10 | The series current is the same everywhere and is never used up; adding a parallel resistor lowers the total resistance; and in parallel the larger resistor carries the smaller current. | All three slips exchange the series rule for current with the parallel rule for voltage. |
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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