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S4 Physics: Circuits in Series and Parallel – Intermediate (10 Questions)
S4 Physics: Circuits in Series and Parallel – Intermediate (10 Questions)
This paper moves into mixed networks and real appliances: two-stage reduction, divider design, heater energy in kWh and joules, internal resistance against efficiency, series lamps at their rating and the effect of a break, instrument connections, and a final item that corrects three reversed statements.
Quick answer The 20 and 30 ohm pair gives 0.2 A with 4 V and 6 V; 20 with 5 ohm gives 4 ohm and 3 A, split 0.6 A and 2.4 A; three parallel resistors give 1.5 ohm and 4 A; the 220 V 2 000 W kettle draws 9.09 A through 24.2 ohm; 8 ohm with the 12 and 24 ohm pair gives 16 ohm, 2 A and 16 V; a divider of 7 and 5 ohm gives 5 V at 1 A; 1 500 W for twenty minutes is 0.5 kWh or 1.8 million joules; 0.6 ohm internal resistance gives 80 percent efficiency; two 6 V 3 W lamps in series take 3 W each and both die on a break; and three connection errors are corrected.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 25 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)
- FoundationA 20 ohm and a 30 ohm resistor are in series across 10 V. Find the current and the voltage across each.
- FoundationA 20 ohm and a 5 ohm resistor are in parallel across 12 V. Find the equivalent resistance, the total current and each branch current.
- FoundationResistors of 6 ohm, 6 ohm and 3 ohm are in parallel across 6 V. Find the equivalent resistance and the total current.
- FoundationAn electric kettle rated 220 V, 2 000 W. Find the working current and the resistance of the element.
- IntermediateAn 8 ohm resistor is in series with the parallel pair of 12 ohm and 24 ohm across 32 V. Find the total current, the parallel voltage and the branch currents.
- IntermediateA 12 V supply feeds two series resistors to give a 5 V output. If the lower resistor is 5 ohm, what should the upper one be and what is the current?
- IntermediateA 220 V, 1 500 W heater runs for 20 minutes. Find the current, the resistance, the energy in kWh and in joules.
- ChallengeA battery of emf 9 V and internal resistance 0.6 ohm drives a 2.4 ohm load. Find the current, terminal voltage and efficiency.
- ChallengeTwo lamps marked 6 V, 3 W are in series across 12 V. Find the current and the power of each, and state what happens to the other lamp if one filament breaks.
- Error redoThree students write that a voltmeter should be connected in series, that an ammeter should be connected in parallel across a component, and that parallel lamps only get the full supply voltage when they are identical. Correct each statement.
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | The total resistance is 50 ohm and the current 0.2 A, giving 4 V across 20 ohm and 6 V across 30 ohm. | The series voltages divide in proportion to resistance and must add up to the supply voltage. |
| 2 | The equivalent resistance is 4 ohm, the total current 3 A, with 0.6 A in the 20 ohm and 2.4 A in the 5 ohm. | The parallel equivalent is smaller than the smallest branch, and the branch currents add up to 3 A. |
| 3 | The equivalent resistance is 1.5 ohm and the total current 4 A. | Add the reciprocals and invert, giving branch currents of 1 A, 1 A and 2 A. |
| 4 | The current is about 9.09 A and the resistance about 24.2 ohm. | Find the current from power and voltage, then the resistance from voltage over current or voltage squared over power. |
| 5 | The parallel pair is 8 ohm, the total resistance 16 ohm and the current 2 A, so the pair carries 16 V and the branches take 1.333 A and 0.667 A. | Reduce the parallel pair first and then treat the circuit as a simple series loop. |
| 6 | The upper resistor should be 7 ohm and the current 1 A. | The divider ratio equals the resistance ratio, and 5 V out of 12 V means the two resistors total 12 ohm. |
| 7 | The current is about 6.82 A, the resistance about 32.3 ohm, and the energy 0.5 kWh or 1.8 million joules. | Energy in kWh is power times hours, with 20 minutes equal to a third of an hour, then multiply by 3.6 million for joules. |
| 8 | The current is 3 A, the terminal voltage 7.2 V and the efficiency 80 percent. | The share of power lost in the internal resistance sets the efficiency, which rises as the internal resistance falls. |
| 9 | Each lamp is 12 ohm, so the total is 24 ohm, the current 0.5 A and each lamp takes 3 W at normal brightness; when one breaks the circuit is open and the other goes out too. | A series circuit offers a single path, so a break anywhere reduces the current to zero. |
| 10 | A voltmeter is connected in parallel and has a high resistance, an ammeter is in series with a low resistance, and every parallel branch has the full supply voltage regardless of whether the lamps match. | All three statements reverse the instrument connection or the parallel voltage rule. |
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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