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Question

A room has AC run hours a day at a voltage of 220V. The wirng of the room consists of Cu of 1mm radius and a length of 10m. Power consumption per day is 10 commercial units . The fraction of it goes in the joule heating in wires is: ρcu=1.7×108Ωm

A
0.32%
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B
0.2%
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C
2%
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D
3.2%
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Solution

The correct option is A 0.32%
Power consumption =10units5hour=2unitshour
=2kw
=2000J/S
So, I=PV
=2000220
=9.09A
Power loss in copper wire =IR
=I2PLA
Power loss in copper wire =9.09×9.09×1.7×108×1017×(103)2
=4.47J
=4.472000×100%
=0.22%
Power loss in aluminium wire =I2R=I2PLA
Power loss in copper wire =9.09×9.09×2.7×108×1017×(103)2
=7.1J
=7.12000×100%
=0.355%
Hence, the answer is 0.355%.

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