Wednesday, 15 May 2013

An electric bulb is rated 220 V and 100 W



Question 3:
An electric bulb is rated 220 V and 100 W. When it is operated on 110 V, the power consumed will be
 
Answer (d): 25w
Solution: R=V2/P
                 = (220)2/100
                 = 484 Ω
The resistance of the bulb remains constant
 if the supply voltage is reduced to 110 V then Vʹ=110 V
 the power consumed by it is given by the expression = Vʹ2/R
                                                                                                         = (110)2/484
                                                                                                         = 25w
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3 comments:

  1. Hiral 7 January 2019 at 22:24

    Why can't we do it by P=VI ......

    ReplyDelete
    Replies
    1. Unknown15 February 2019 at 07:20

      I have the same doubt

      Delete
    2. Unknown8 March 2019 at 14:41

      Because current changes with change in potential difference but the resistance of the appliance will remain the same

      Delete

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