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Electricity

Scorching goIITian

Joined:	15 Jul 2007
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9 Mar 2009 12:27:16 IST

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247

Power

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Q. A battery of internal resistance is connected to a variable resistor whose value can vary from to . The resistance is initially set at . If the resistance is now increased then :

a) power consumed by it will decrease

b) power consumed by it will increase

c) power consumed by it may increase or may decrease

d) power consumed will first increase then decrease

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JPS

Blazing goIITian

Joined: 21 Nov 2008

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9 Mar 2009 12:41:51 IST

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the battery will give a constt. potential difference of V=E- ir....... now power P = V^2/R where R = resis. of resistor. so, when R increases P decreases .....so power consumed by it will decrease.....tel me if i am right...

Bhaskar Tetarbe

Scorching goIITian

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9 Mar 2009 12:47:16 IST

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Your answer seems okay, but there are more finer points to this. I f you know the graph between Power and external resistance you would very well understand that its not necessary that with increase in external resistance power decrease.

Can you prove your assumption mathematically ?

rahul gaadhe

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Joined: 21 Jan 2009

Posts: 90

9 Mar 2009 12:48:30 IST

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let the battery be v volt & resistance r ohm (4<r<10)

current in circuit=v\r+2

power consumed by r=v²r\(2+r)² which is dec. fⁿ

so ans is a)

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