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

(a) The resistance of an electric appliance is given by:
`R=V_(s)^(2)/W`,so, `R=(200)^(2)/1000 = 40 Omega`
(b) The actual power consumed by an electric appliance is given by
`P=(V_(A)/V_(s))^(2) xx W`
so, `P=(100/200)^(2) xx 1000 = 250 W`
( c) The total electrical energy consumed by an electric appliance in a specific time is given by,
`E =(sumW_(1)h_(1))/1000 kWh`
So, `E=(1000 xx (10 xx 30))/1000 = 300 kWh`