Question

A household has a 100 W lamp lighted for 2 hours, two 60 W lamps lighted for 4 hours and an electric fan of 50 W working for 8 hours a day. Calculate the electric units consumed each day.

Explain with complete calculations & justifications.

Answer 1

ENERGY = POWER x TIME

electrical energy consumed by :-

1)one 100W lamp
= (100 x 2 )Wh
= 200 wh

2)two 60 W lamp
=( 60 x 4)Wh
= 240 Wh

3)one fan of 50 W
= (50 x 8) Wh
= 400 Wh

the electrical unit consumed
=( 200 + 240 + 400)Wh
= 840 Wh

Answer 2

we know
energy = power x time

energy consume by household lamp light =100w x 2hour = 100 x 3600 x 2 Joule
=7.2 x 10^5 Joule

energy consume by two another lamp light = (60 x 2 ) w x 4 hrs
=120 x 3600 x 4 Joule
=480 x 3600 Joule
=1728000 Joule
=17.28 x 10^5 Joule

energy consume by electric fan =50w x 8hrs =50 x 8 x 3600 Joule
= 400 x 3600 Joule
=144 x 10^4 Joule
=14.4 x 10^5 Joule

now ,
total energy consume per day =( 7.2 x 10^5 + 17.28 x 10^5 + 14.4 x 10^5 ) Joule
=(7.2 +17.28 +14.4) x10^5 Joule

we know ,
1kwh = 3.6 x 10^6

so,
total energy consume per day
=(7.2 +17.28 +14.4) x10^5/3.6 x 10^6 kwh

=(2 +4.8 + 4) x 10^-1 kwh
=10.8 x 10^-1 kwh
=1.08 kwh