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A lamp can work on a 50 volt main taking...

A lamp can work on a 50 volt main taking 2 amps. What value of the resistance must be connected in series with it so that it can be operated from 200 volt mains giving the same power.

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Lamp voltage, V=50V and Current.I=2amps
Resistance of the lamp=V/I=50/2=`25Omega`
Resistance connected in series with lamp=r
Supply voltage=200 volt and Circuit current I=2A
Total resistance Rt=V/I=200/2=100`Omega`
`Rt=r+r=100=25+r=r=100-25=75Omega`
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