Question

A 100 watt electric bulb is lighted for 2 hours daily and four 40 watt bulbs are lighted for 4 hours everyday.Calculate the energy consumed(kwh)in 30 days?

Answer 1

According to the question,

100 W = 100 joules per second
1 watt hour = 3600 joules .... (1)
The light bulb is lighted for two hours therefore,

100W × 2 hours = 200 watt hours

200 watt hours = 720000 joules .... ( using- 1)

1 KWh = 3600000 joules. .....(2)

Units consumed per day = 720000 ÷ 3600000
= 0.2 units .....(using- 2)

Units consumed in a month = 0.2 × 30 = 6units

Now,
Sum of power of four 40 watt bulbs = 160W

160watt × 4hours = 640 watt hours

640 watt hours = 2304000 joules ...(using 1)

Energy consumed per day =
2304000÷3600000 = 0.64 units ...(using- 2)

Energy consumed in a month = 0.64× 30 = 19.2

Total energy consumed in a month = 19.2 + 6
= 25.2 units

I hope this'll​ help you.

Answer 2

Solution :

Power of electric bulb = 100 watt = 0.1 Kwh

Time = ( 2 × 30 ) = 60 hours

Energy consumed = Power × time

⇒ Energy = 0. 1 × 60 = 6 units.

Now,

Power of 4 bulbs = ( 4 × 40 ) = 160 watt

= 1.6 Kwh.

Time = ( 4 × 30 ) = 120 hrs.

Energy consumed = P × T

⇒ Energy = 1.6 × 120 = 192 units.

Total energy consumed = ( 6 + 192 ) units

⇒ Total Energy = 199 units.

Hence, the total energy consumed is 199 units.