Question

A fan of resistance 400 ohm is connected to a 220 V power supply. The rate of energy consumed by the bulb is?

a) 65 W
b) 86 W
c) 121 W
d) 148 W
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Answer 1

Correct question :

A fan of resistance 400 ohm is connected to a 220 V power supply. The rate of energy consumed by the fan is?

a) 65 W

b) 86 W

c) 121 W

d) 148 W

SOLUTION :

Given :

• Resistance of fan = 400 Ω
• Power supply = 220 V

To find :

Rate of energy consumed by fan

Solution :

• Rate of energy consumed means energy consumed per unit times.
• Energy consumed is equal to work done, this gives , rate of energy consumed = rate of work done.
• Rate of work done is called power.

So in this question to find , Rate of energy consumed we will find power of fan.

• For a resistance R, connected to potential difference V , power ( P) is given by -

P = V² ÷ R

Therefore,

Rate of energy consumed by fan = Power of fan

➝ Rate of energy consumed by fan = (220)² ÷ 400 W

➝ Rate of energy consumed by fan = 48400 ÷ 400 W

➝ Rate of energy consumed by fan = 484 ÷ 4 W

➝ Rate of energy consumed by fan = 121 W

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ANSWER :

Option (c) 121 W