Question

(a) Define power. What is the S.I. unit of power and commercial unit of power? 

(b) A tube light of 80 W is used for 8 hours per day. Calculate the unit of energy consumed in 1 day by the tube light.

Answer 1

(a) Power is the rate of doing work.

S.I. unit of power = watt

1 watt = \(\frac { 1J }{ 1s }\)

Commercial unit of power kWh

1kWh = 3.6 x 10⁶ Joules.

(b) Power of electric tube light = 80 

=0.08 kW

Time used = 8 hour

Energy = power x time taken = 0.08 x 8

= 0.64 kWh

= 0.64 units.

∴ The energy consumed per day = 0.64 units.