Question

An electric bulbis marked 250W, 230V
i) How much energy in joules does it consume in 1 hour?
ii) how long would this lamp take to use 1kWh energy when connected to 230 V mains?​

Answer 1

Answer:

Power (P) = 250 W

Voltage (V) = 230 V

(i) We know that,

W (energy consumed) = P×t

Given, t= 1h

Covert the hour into seconds since Joule = watt×sec

t=60×60 seconds

= 3600 seconds.

Now,

W= P×t

= 250×3600

= 9 × 100000 J

(ii) we know,

Energy (in kWh) = (V×Ixt)/1000

We don't have I (Ampere), therefore

I = P/V

= 250/230 A

= (Lets just keep it this way) 25/23 A

Now, given energy = 1 kWh

1 kWh= (230×25xt)/1000×23

=> (1000×23)/230×25= t

=> 4 hours = t