Question

Calculate the electricity bill amount for a month of $30$ days, if the following devices are used as specified:
A) $4$ bulbs of $60W$ for $6$ hours.
B) $3$ tube lights of $40W$ for $8$ hours.
C) A refrigerator of $300W$ for $24$ hours.
D) An electric mixer of $750W$for $1$hour.
E) A T.V. of $100W$ for $6$hours.
The cost per unit of electricity consumed is $Rs.3$ for every unit. Find an electricity bill.

Answer 1

Power is the rate at which the electrical energy is transferred from an electric circuit. It is helpful in determining the efficiency of an electric circuit. Electric power is defined as the rate at which the work is done. It is measured in the units of Watts.

Complete step by step solution:
The formula for power is
$Power = \dfrac{{EnergyUsed}}{{Time}}$
Or $Energy = Power \times Time$---(i)
Number of Bulbs $= 4$
Power consumed $= 60W$
Time taken $= 6hours$
Substituting the value in equation (i), the energy consumed by bulbs is
$Energy = 4 \times 60 \times 6 = 1440W/hr$
Number of tube lights $= 3$
Power Consumed $= 40W$
Time taken $= 8hours$
The energy consumed by tube lights is
$\therefore Energy = 3 \times 40 \times 8 = 960W/hr$
Power consumed $= 300W$
Time taken $= 24hours$
Energy consumed by refrigerator is
$\therefore Energy = 300 \times 24 = 7200W/hr$
Power Consumed $= 750W$
Time taken $= 1hour$
Energy consumed by electric mixer is
$\therefore Energy = 750 \times 1$
Power consumed $= 100W$
Time taken $= 6hours$
Energy consumed by T.V. is
$\therefore Energy = 100 \times 6 = 600W/hr$
Total power consumed will be the sum of the individual power consumed by all the appliances and is calculated as$= 1440 + 960 + 7200 + 750 + 600$
$\Rightarrow 10950W/hr$
Energy consumed per day will be $= 10.9kW/hr$
Energy consumed per month $= 10.9 \times 30 = 327kW/hr$
$\therefore$ Cost per unit electricity consumed is $= 3 \times 327 = 981Rs$
$\Rightarrow$The electricity bill is $= 981Rs$.

Note: It is also to be noted that energy transfer is the work done. If the value of power is large it means that a large amount of energy is consumed in a very short period of time. Energy means the ability to do some activity or work. It can neither be created nor destroyed but can be transformed from one form to another. But power is the rate of conversion of energy. It has only magnitude and not direction. So it is a scalar quantity.