Question

Calculate the units of electricity consumed in the month of September form the following details.
(i) One 40 W bulb used for 5 hours daily.
(ii) One 100 W bulb used for 4 hours daily.
(iii) One 240 W electric fan used for 4 hours daily.
Also calculate the monthly bill at the rate of Rs 3 per unit.

Answer 1

Electric energy = electric power `xx` time
`E = pt`
(i) Electric bulb
`E_(b) = 40 W xx 5 h`
`= 0.40 xx 5 = 0.2 kWh`. Thus, the bulb consumes 0.2 unit daily
There are 30 days in the month of September
`:.` Energy consumed by the bulb for 30 days is `0.2 xx 30 = 6 kWh` or `6` units.
(ii) Electric bulb
`E_(B) = 100 W xx h`
`= 0.1 xx 4 = 0.4 kW h = 0.4` units daily
For 30 days `E_(r) = 0.4 xx 30 = 12 kWh = 12` units.
(iii) Electric fan
`E_(h) = 240 W xx 10 h = 2.4 kWh = 2.4` units daily
For 30 days, `E_(h) = 24 xx 30 = 72` units
Total energy consumed in the month of November is `E_(b) + E_(B) + E_(h) = 6+12+72 = 90` units
The cost of electricity is `₹ 3` per unit
Energy consumed is 90 units
`:.` Monthly bill for November `= 90 xx 3 = ₹ 270`