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S3 Physics: Household Electricity, Power and Cost (10 Error-Correction Items)
S3 Physics: Household Electricity, Power and Cost (10 Error-Correction Items)
Ten error-correction items revisiting unit conversion, bills, current and fuse choices.
Drill Focus Write the units before substituting numbers; never mix W with kW or J with kWh.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 30 |
| Difficulty mix | Error redo 10 |
| Chapter | Chapter: S3 Physics: Household Electricity, Power and Cost |
| Level | S3 |
02 Questions (10 items)
- Error redoA 1500 W kettle runs for 0.4 h. How much energy is used in kWh, and what is the cost at 1.2 dollars per unit?
- Error redoA 100 W lamp is on for 8 h a day. What is the daily energy use in kWh, and the cost at 1.2 dollars per unit?
- Error redoA 2 kW air conditioner runs for 2.5 h. How much energy is used in kWh, and what is the cost at 1.2 dollars per unit?
- Error redoA bill of 9 dollars covers 7.5 units. What is the price per unit?
- Error redoHow many kWh are 3.6×10⁶ J and 7.2×10⁶ J?
- Error redoA 2 200 W appliance is connected to 220 V. What is the current, and is a 13 A fuse enough?
- Error redoTwo appliances of 800 W and 1 200 W share a 220 V board. What is the total current to two decimal places?
- Error redoA 100 W fan runs 8 h a day for 30 days. What is the energy use in kWh, and the cost at 1.2 dollars per unit?
- Error redoA 500 W appliance needs 1.5 kWh of energy. For how many hours must it run?
- Error redoA 2 500 W heater runs for 2 h and a student answers 5 000 kWh. What is the correct energy use and the mistake?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 0.6 kWh; 0.72 dollars. | Divide the watts by 1000 to get kW, then multiply by the hours. |
| 2 | 0.8 kWh; 0.96 dollars. | Convert watts to kW, multiply by the hours, then by the tariff. |
| 3 | 5 kWh; 6 dollars. | The power is already in kW, so multiply by the hours without dividing again. |
| 4 | 1.2 dollars. | Divide the bill by the number of units to get the price per unit. |
| 5 | 1 kWh and 2 kWh. | One kWh is 3.6×10⁶ J, so divide the joules by that value. |
| 6 | 10 A; yes. | Use I = P ÷ V; a current below the fuse rating is safe. |
| 7 | About 9.09 A. | Add the powers first, then divide by the voltage. |
| 8 | 24 kWh; 28.8 dollars. | Multiply power, hours and days, converting watts to kW first. |
| 9 | 3 hours. | Time is energy divided by power; unify the units first. |
| 10 | 5 kWh; the watts were never divided by 1000. | Watts times hours give Wh; divide by 1000 for kWh, or the answer is 1000 times too large. |
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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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.