A room has AC run for 5 hours a day at a voltage of 220V. The wiring of the room consists of Cu of 1 mm radius and a length of 10 m. Power consumption per day is 10 commercial units. What fraction of it goes in the joule heating in wires? What would happen if the wiring is made of aluminum of the same dimensions?
[ρcu = 1.7 × –810Ωm, ρAl = 2.7 × 10–8 Ωm]
Given:
Power consumption for 5 hours = 10 units
Power consumption for 1 hour = 2 unit = 2000J/s
Radius of wire = r = 1mm
Length of wire = l = 10m
We know
I 
9A
Resistance in copper wire 
Power lost as heat in copper wire
Fractional loss in copper wire 
Power lost as heat in aluminum wire 
Fractional loss in aluminium wire 
1