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  4. 3 identical bulbs are connected in series and these together dissipate a power P. If now the bulbs are connected in parallel, then the power dissipated will be :

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Q. 3 identical bulbs are connected in series and these together dissipate a power P. If now the bulbs are connected in parallel, then the power dissipated will be :

MGIMS WardhaMGIMS Wardha 2006

Solution:

Let the resistance of each bulb is R. Then, total resistance in series $ =3R $ $ \therefore $ $ P=\frac{{{V}^{2}}}{3R} $ In parallel, total resistance $ =\frac{R}{3} $ $ \therefore $ Power dissipated $ P'=\frac{{{V}^{2}}}{R/3} $ $ =\frac{3{{V}^{2}}}{R} $ $ =9\left( \frac{{{V}^{2}}}{3R} \right) $ $ =9P $