Question

An electric bulb I rated 200 v and 100 w what is it's resistance 5 such bulbs burn for 4 hours then what is the electrical energy consumed and calculate the cost if the rate rupees 5 per unit

Answer 1

Using, P = V 2/ R

we get R = V2/ P

= (200)2/ 100

= 400  

Energy consumed = P x t

= 400 x 5

= 2000 Wh

=2KWH

Cost at the rate of 5 RUPEES per unit = Rs (5 x 2)

= 10

Answer 2

Given :

Power rating of the electric bulb ( P ) = 100 W .

Potential difference of the bulb ( V ) = 200 v .

Resistance of the bulb ( R ) = ?

We know that Power = V²/R according to the formula of power .

⇒ R = V²/P

Putting the values of P and V we get :

⇒ R = ( 200 )² / ( 100 ) Ω

⇒ R = ( 200 × 200 ) / ( 100 ) Ω

⇒ R = 200 × 2  Ω

⇒ R = 400 Ω

The resistance will be 400 Ω .

Power rating of the bulb is given as 100 W .

Time taken by the bulb is 4 hr .

We know that Power = work / time

⇒ Work = power × time

⇒ Work = 100 W × 4 hr

⇒ Work = 400 Whr .

The electrical energy is just the capacity of doing work .

The electrical energy consumed will be 400 W hr .

400 Whr = 0.4 kWhr .

The cost is at the rate of Rupees 5 per 1 kWhr .

This means that the cost for 400 W hr or 0.4 kWhr will be :

Rs 5 × 0.4

⇒ Rs 2

Rs 2 will be the cost of electrical energy .