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CBSE Class 10 Science Question 3 of 41

Electricity — Question 3

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Question

Question 3

An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be ...............

  1. 100 W
  2. 75 W
  3. 50 W
  4. 25 W
Answer

25 W

Reason —

Given, V = 220V ; P = 100 W ; R = ?

We know,

⇒P=V2R⇒R=V2P\phantom{\Rightarrow} \text{P} = \dfrac{\text{V}^2}{\text{R}} \\[1em] \Rightarrow \text{R} = \dfrac{\text{V}^2}{\text{P}}

Substituting the values, we get

R = 2202100\dfrac{\text{220}^2}{\text{100}} = 484 Ω

When voltage is reduced, resistance remains the same. Hence, the power consumed :

P = 1102484\dfrac{110^2}{484} = 25 W

Hence, the power consumed = 25 W.