Q1. [3] medium exam-ready
(a) Define electric power and write its SI unit.
(b) A household uses the following appliances: one 1000 W electric iron for 2 hours, two 60 W fans for 5 hours, and one 100 W television for 4 hours every day. Calculate the total electrical energy consumed in one day in kWh.
Generated by claude-sonnet-4-6 · 2026-06-26 01:09 · grounding rag
Model Answer
(a) Electric power is the rate at which electric energy is consumed (or dissipated) in a circuit. It is given by $P = VI$.
SI unit: Watt (W). 1 W = 1 V × 1 A.
(b)
| Appliance | Power × Time | Energy |
|---|---|---|
| Electric iron | 1000 W × 2 h | 2000 Wh |
| Two fans | 2 × 60 W × 5 h | 600 Wh |
| Television | 100 W × 4 h | 400 Wh |
Total energy = 2000 + 600 + 400 = 3000 Wh = 3 kWh
Source: Chapter 11 – Electric Power, Section 11.8
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Explanation
- For part (a), define power as rate of energy consumption and state the unit; both are needed for full marks.
- For part (b), calculate energy for each appliance separately (Energy = Power × Time), sum them, then convert Wh → kWh by dividing by 1000. Don't forget the fans are two in number — multiply the 60 W by 2. Showing a clear table or stepwise working fetches full marks.