Electrical energy consumption and electrical tariffs numerical.

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In a house 6 bulbs each of 100 watt runs for 8 hours daily and 3 heaters of 1500 watt runs for 5 hours daily, how much unit of electricity is consumed in thirty days?

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Solution
Given
Bulbs:
Number of bulbs, N(Bulbs) = 6
Power of 1 bulb, P(Bulbs) = 100 W
Power of 1 bulb in kilowatt, P(Bulbs) = 100/1000 KW = 0.1 KW
Time for which it runs daily, T(Bulbs) = 8 hours.
Energy consumed by 1 bulb per day in KWh =  0.1KW x 8h = 0.8 KWh
Energy consumed by 6 bulbs per day in KWh = 6 x 0.8 KWh = 4.8 KWh
Energy consumed by 6 bulbs in 30 days, E(Bulbs) = 4.8 x 30 KWh = 144 KWh.

Heaters:

Number of heaters, N(Heaters) = 3
Power of 1 heater, P(Heaters) = 1500 W
Power of 1 heater in kilowatt, P(Heaters) = 1500/1000 KW = 1.5 KW
Time for which it runs daily, T(Heaters) = 5 hours.
Energy consumed by 1 heater per day in KWh =  1.5KW x 5h = 7.5 KWh
Energy consumed by 3 heaters per day in KWh = 3 x 7.5 KWh = 22.5 KWh
Energy consumed by 3 heaters in 30 days, E(Heaters) = 22.5 x 30 KWh = 675 KWh.

Total energy consumed in 30 days, E = E(Bulbs) +  E(Heaters)

=  144 KWh + 675 KWh

= 819 KWh

We know that,

1 unit of electricity = 1 KWh

So total units of  electricity consumed in 30 days is 819 units.

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For a TV rated 220V and 80w. How many units of electricity is consumed if the TV is run for one month 4 hours daily?

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Rated power of the TV, P = 80w
Rated voltage of the TV, V = 220V
Time in hours for which TV runs everyday = 4 hrs
Number of days in a month = 30 days
time in hours for which the TV runs in a month, T = 30 x 4 hrs = 120 hrs
Energy consumed by TV in 1 month, 
E = P x T
  = 80 w x 120 hrs
  = 9600 watt-hours
Energy consumed expressed in kWH 
= 9600/1000 kWH
= 9.6 kWH

As we know 1 unit of electricity is equal to 1 kWH

So, the TV consumes 9.6 units in one month.

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10 tube lights of 20 W each are used in a house for 5 hours daily, calculate the bill of one month for the electricity with the rate of Rs. 7.30 per unit.

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Solution

Given

Numbers of tube lights, N_tube  =  10

Power rating of each tube light, P_tube  =  20 W

Time duration of use of each tube light per day, T_day  =  5 hours

Time duration of use of each tube light in a month, T_month  =  5*30 hours

                    = 150 hours

Energy consumed by each tube light in a month, E_tube  =  P_tube*T_month

                    =  20 W * 150 hours = 3000 watt-hours

Energy consumed by each tube light in a month in terms of KWh, E_tube,KWh  =  E_tube/1000

                    =  3000 watt-hours/1000  =  3 KWh = 3 units.    (∵ 1 unit = 1 KWh)


Total KWh consumed by 10 tube lights in 1 month, E_Total  =  N*E_tube,KWh  =  10*3 units = 30 units.


Electricity rate = Rs. 7.3 per unit.

Total electricity bill = E_Total,KWh * Electricity rate

                  = 30 units * Rs. 7.3 per unit

                  = Rs. 219

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An electric bulb draws a current of 0.8 A from 220 V main line. The bulb is used 8 hours daily, calculate the total bill for 30 days, if per unit costs Rs. 7.0.

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Solution

Given

Current drawn by electric bulb, I_bulb  =  0.8 A

Voltage supplied to the electric bulb, V_bulb  =  220 V

Time duration of use of bulb per day, T_day  =  8 hours

Time duration of use of bulb in a month, T_month  =  8*30 hours

                    = 240 hours

Power rating of electric bulb, P_bulb  =  I_bulb * V_bulb

            = 0.8 A * 220 V = 176 watts

Energy consumed by bulb in a month, E_bulb  =  P_bulb*T_month

                    =  176 W * 240 hours = 42,240 watt-hours

Energy consumed by bulb in a month in terms of KWh, E_bulb,KWh  =  E_bulb/1000

                    =  42,240 watt-hours/1000  =  42.24 KWh = 42.24 units.    (∵ 1 unit = 1 KWh)


Electricity rate = Rs. 7 per unit.

Total electricity bill = E_bulb,KWh * Electricity rate

                  = 42.24 units * Rs. 7 per unit

                  = Rs. 295.68