Question

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be : (a) 100 W (b) 75 W (c) 50 W (d) 25 W​

Answer 1

Answer :-

Required power consumed by the electric bulb is 25 W [Option.d] .

Explanation :-

We have :-

→ Initial voltage (V) = 220 V

→ Initial power (P) = 100 W

→ New voltage (V') = 110 V

To find :-

→ New power (P') .

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Firstly, let's calculate the resistance of the electric bulb .

P = V²/R

⇒ 100 = (220)²/R

⇒ 100R = 48400

⇒ R = 48400/100

⇒ R = 484 Ω

We have got the resistance of the bulb . Now, we can calculate the new power consumed .

P' = (V')²/R

⇒ P' = (110)²/484

⇒ P' = 12100/484

⇒ P' = 25 W

Answer 2

Given :-

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V

To Find :-

Power

Solution :-

We know that

P = V²R

I n C a s e 1 :

Potential difference = 220 V

Power = 100 W

100 = (220)²/R

100 = 48400/R

48400/100 = R

484 = R

I n C a s e 2 :

Potential difference = 110 V

Resistance = 484 ohm

P = V²/R

P = (110)²/484

P = 12100/484

P = 25 W

Therefore,

Option D is correct