Question

1. why does the cord of an electric heater not glow while the heating element does?
2. An electric heater rated 800 w operated 6 hour per day. find the cost to operate it for 30 days at Rs.300 per unit.
3. An electric motor takes 5 A from a 220v line. determine the power of the motor and the energy consumed in 2 hour?

Answer 1

1)ans=The heating element of the heateris made up of alloy which has very high resistance so when current flows through the heating element, it becomes too hot and glows red. But the resistance of cord which is usually of copper or aluminium is very law so it does not glow.
2)ans=Energy=power*time=0.8(kw)*6(hr)=4.8kwh

Energy used in a day=4.8kwh=4.8 unit

Energy used in 30 days= 144 unit

Total cost=144*3=432 rs

3)ans=given I = 5A
        V = 220V
∴ power = V*I
             = 5*220  
             = 1100 W
             = 1.1kW
Energy consumed = Power*Time
                           = 1.1*2
                          = 2.2 kW*hr

Answer 2

First question answer.

Hope it's helpful for you.