Question

an electric bulb rated at 220 volt 100 words what is its resistance 5 such balls burn for 4 hours what is the electrical energy consumed calculate the cost if the rate is 50 pause per unit

Answer 1

First of all manage your auto correct..

And here's what I think,

P = V 2/ R
So we get R = V2/ P
= (200)2/ 100
= 400 
Now, Energy consumed = P x t
= 100 x 4
= 400 Wh
= 0.4kWh
Cost at the rate of 50 paise per unit = Rs (0.50 x 0.4)
= Rs 2

Answer 2

Using ohms law

Current (l) =voltage (v) /resistance (R)

Therefore R=V/I

While power p=current(l) x voltage (v)

That means I=p/v

Hence R=V2/p

=220squared/100

=48400/100

=484ohms
Energy consumed by 5bulbs in 4hrs

Energy =power x time (while power per each bulb is 100watts or 100j/sec)

Energy consumed by 1bulb
If 1sec=100jolus

Then 40x60x60=(100x40x60x60)/1j

=14400000joules

=14400k/joules

Then 5bulbs=5x14400

=72000kj(this amount of energy consumed)

COST

1BULb=100watts

Then 5=500watts

1unit of electricity =1kw

If 1kw(1000w)=50paise

=500x50/1000

=25paise