Question

An electric bulb is rated 250 W, 230 V. 

1. the energy consumed in one hour, and
2. the time in which the bulb will consume 1.0 kWh energy when connected to 230 V mains.

Answer 1

(i) Given, Power (P) = 250 W, Voltage (V) = 230 V, Time (t) = 1 h = 3600 sec, Energy (E) = ?

Energy, E = P × t

Substituting the values in the formula above, we get,

E = 250 × 3600

E = 9 × 10⁵ J

(ii) Let t be the time in which the bulb will consume 1.0 kWh energy when connected to 230 V mains.

P = 1.0 kWh = 1000 Wh

Substituting the value in the formula, we get,

⇒ 1000 = 250 × t

⇒ t = `1000/250`

⇒ t = 4 h

Hence, time = 4 h