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Physics

A bulb is rated 100 W-220 V. It is being used at 110 V supply. The power consumed by bulb is:

  1. 100 W
  2. half of 100 W
  3. nearly 25 W
  4. none of the above

Current Electricity

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Answer

nearly 25 W

Reason — Given,

Power (P) = 100 W

Voltage (V) = 220 V

We know that,

Power (P) = VI

Substituting the values in the formula above, we get,

100=220×I⇒I=100220⇒I=0.45A100 = 220 \times I \\[0.5em] \Rightarrow I = \dfrac{100}{220} \\[0.5em] \Rightarrow I = 0.45 A

Hence, current through the lamp = 0.45 A

Power consumed when voltage is 110 V = ?

Resistance of lamp (R) = V2P\dfrac{V^2}{P}

Substituting the values in the formula, we get,

R=2202100⇒R=484ΩR = \dfrac{220^2}{100} \\[0.5em] \Rightarrow R = 484 Ω

From relation,

P = V2R\dfrac{V^2}{R}

Substituting the values in the formula, we get,

P=1102484⇒P=25WP = \dfrac{110^2}{484} \\[0.5em] \Rightarrow P = 25 W

Hence, power consumed is 25 W

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