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

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NCERT Question 3 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 Explanation: The resistance of the bulb would remain constant even when voltage supply is changed. Given Potential difference = V = 220 V Power = P = 100 W Finding resistance We know that P = V I Putting I = š‘‰/š‘… P = V Ɨ š‘‰/š‘… P = š‘‰^2/š‘… R = š‘‰^2/š‘ƒ R = (220)^2/100 R = (220 Ɨ 220)/100 R = 22 Ɨ 22 R = 484 Ī© When V = 110 V Pā€™ = š‘‰^2/š‘… Pā€™ = (110)^2/484 P = (110 Ɨ 110)/484 P = 12100/484 P = 1100/44 P = 100/4 P = 25 W Correct answer is (d) 25 W

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CA Maninder Singh is a Chartered Accountant for the past 13 years and a teacher from the past 17 years. He teaches Science, Economics, Accounting and English at Teachoo