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S1 Science: Energy Forms and Conversion (Paper 4: mistake clinic)
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S1 Science: Energy Forms and Conversion (Paper 4: mistake clinic)
This last paper revisits three frequent errors: minutes read as hours, watts read as kilowatts, and the useful output mistaken for the input.
Direct answers Spend three seconds checking those three points after each question, which beats rereading the notes.
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: S1 Science: Energy Forms and Conversion |
| Level | S1 Science |
02 Questions (10 items)
- FoundationOne watt equals how many joules each second?
- FoundationWhat energy conversion happens inside a dry cell?
- FoundationDoes conservation of energy mean no energy ever becomes waste heat?
- IntermediateA machine is 50 per cent efficient on 400 J. What are the useful output and the waste?
- IntermediateHow much does 0.5 kWh cost at $1.2 per kWh?
- Intermediate800 J of energy is converted in 4 seconds. What is the power?
- ChallengeA 60 W lamp runs for 30 minutes at $1.2 per kWh. What is the cost?
- ChallengeA 100 W lamp, a 200 W fan and a 700 W cooker run together for 2 hours. What is the energy and the cost at $1.2 per kWh?
- ChallengeA machine is 80 per cent efficient on 1 500 J. What are the useful output and the waste?
- Error redoA student works out that a 40 W lamp for 10 hours uses 400 kWh. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 1 J/s | The watt is defined as one joule per second. |
| 2 | Chemical energy changes into electrical energy | A chemical reaction inside the cell turns stored chemical energy into electrical energy that drives the circuit. |
| 3 | No, energy may become waste heat and only the total stays the same | Conservation concerns the total and not the usefulness, and waste heat is exactly how energy slips away. |
| 4 | Useful 200 J and waste 200 J | Half of 400 J is 200 J useful, and the other 200 J is lost. |
| 5 | $0.60 | Half a kilowatt hour times 1.2 gives $0.60, so the sum is a direct multiplication. |
| 6 | 200 W | 800 divided by 4 is 200 W. |
| 7 | About $0.04 | That is 30 Wh or 0.03 kWh, and 0.03 times 1.2 gives $0.036, roughly four cents. |
| 8 | 2 kWh and $2.40 | The total is 1 000 W or 1 kW, so 1 times 2 gives 2 kWh and 2 times 1.2 gives $2.40. |
| 9 | Useful 1 200 J and waste 300 J | 80 per cent of 1 500 J is 1 200 J, and the remaining 300 J is wasted. |
| 10 | The division by 1 000 was skipped, so the answer is 0.4 kWh | 40 W for 10 hours is 400 Wh or 0.4 kWh, costing about $0.48. |
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.
Keep three columns in the error log: question, cause, corrected steps. The three commonest slips are reading minutes as hours, watts as kilowatts, and taking high power for high efficiency.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.