Question

An electric oven is marked 1000 W – 200 V. Calculate:

1. The resistance of its element.
2. Energy consumed by the oven in `1/2` hour in joules.
3. Time, in which it will consume 15 kWh of energy.

Answer 1

P = 1000 W; V = 200 V

(a) Resistance of its element:

\[R = \frac{V^2}{P}\]

\[= \frac{(200)^2}{1000}\]

\[= \frac{40000}{1000}\]

\[= 40\Omega\]

(b) Energy consumed by the oven in `1/2` hour:

\[t = \frac{1}{2}\text{ h} = 1800\text{ s}\]

\[E = P \times t\]

\[= 1000\text{ W} \times 1800\text{ s}\]

\[= 1800000\text{ J}\]

(c) Time in which it will consume 15 kWh of energy:

\[E = 15\text{ kWh} = 15000\text{ Wh}\]

\[P = 1000\text{ W} = 1\text{ kW}\]

\[t = \frac{E}{P}\]

\[= \frac{15}{1}\]

\[= 15\text{ h}\]