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10 Oct 2011 20:17:01 IST

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A water heater is marked 1500W, 220V. If the voltage drops to 180V,calculate the power c

Physics

A water heater is marked 1500W, 220V. If the voltage drops to 180V,calculate the power consumed by the heater.

P₁=V₁I, 1500=220*I Hence I=150/22..............................(1)

P₂= V₂i P₂=180*150/22 from (1)

Hence P₂ =1227.27 W

(or)

P₁=V₁I, P₁=V₁²/R..................(1)

P₂=V₂I,P₂=V₂²/R....................(2)

P₁/P₂=V₁²/ V₂²

P₂=P₁*V₂²/V₁²

P₂=1500*(180)2/(220)2

P₂=1004.13W

WHICH OF THE ABOVE METHODS ARE CORRECT AND WHY?? CAN U PLEASE EXPLAIN???

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edison

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Joined: 19 Oct 2006

Posts: 7537

26 Jan 2012 19:06:59 IST

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Second method is correct as here the resistance of the heater device is constant and the quantity that changes is potential difference and current passing through the heater. Thus second method is correct as it takes care of this constraint.

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