A ` 1 k W` heater is meant to operate at `200 V`.
(a) What is the resistance?
(b) How much power will it consume if the line voltage drops to `100 V`?
( c ) How many units of electrical energy will it consume in a month `( of 30 days)` if it operates `10 h `daily at the specified voltage `( 200 V)`?

Explanation

Here, power of electric heater,
P = 1 kW = 1000 W , V = 220V
(i) Resistance of heater,
`R = V^(2)/P = (220)^(2)/1000 = 48.4 Omega`
(ii) Current drawn by heater,
`I= P/V = 1000/220 = 4.545 A`
(iii) Rate of dissipation of energy,
`H = P/J = 1000/4.2 = 238.1 cal.s^(-1)`
(iv) New power of heater `= (V_(1)^(2))/R = (200)^(2)/48.4`
`= 826.45 W`