Science (086) — CBSE Class 10 board question

(i) Electric power is the rate at which electrical energy is consumed (or dissipated) in a circuit.
$$P = \frac{W}{t} = VI$$
SI unit: Watt (W)

(ii) Given: V = 220 V, P₁ = 100 W, P₂ = 60 W

Current drawn by 100 W bulb:
$$I_1 = \frac{P_1}{V} = \frac{100}{220} \text{ A}$$

Current drawn by 60 W bulb:
$$I_2 = \frac{P_2}{V} = \frac{60}{220} \text{ A}$$

Total current from mains:
$$I = I_1 + I_2 = \frac{100}{220} + \frac{60}{220} = \frac{160}{220} \approx 0.727 \text{ A}$$

The current drawn from the mains is approximately 0.73 A.

Source: Chapter 11 – Electricity, Exercise Q.15

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• For (i), always state the formula along with the definition; examiners expect both for 1 mark.
• For (ii), the key idea is that in a parallel circuit each bulb gets the full 220 V. Use $I = P/V$ for each bulb, then add the currents. This directly matches Exercise Q.15 in the textbook.
• Do not find resistance first unless asked — the $I = P/V$ route is faster and cleaner.