Electrical energy costs 25 paisa per kilowatt hour. Assuming that no energy is wasted, the cost of heating 4.6 kg of water from `25^(@)C` to the boiling point is

Options

A. 25 paisa
B. 50 paisa
C. 20 paisa
D. 10 paisa

Answer

D

Explanation

Here, electric energy cost in Rs. = 25 paisa / kWh,
mass of water, m = 4.6 Kg
initial temperature of water,
and `T_(f) =` boiling point of water `=100^(@)C`
As heat used by water to boil,
`Q=ms(T_(f)-T_(i))`
So, `Q=4.6 times 4.2 times 10^(3) times (100-25)`
`(because` Specific heat of water, `S=4.2 times 10^(3)J" "kg^(-1@)C)`
`rArr " "Q=1499 times 10^(3)J`
`therefore` Number of units of electric energy,
`" "N=Q/(1kWh)=(1499 times 10^(3))/(3.6 times 10^(6))`
`" "(because 1kWh=3.6 times 10^(6)J)`
`rArr " "N=0.40` unit
Cost of electric energy in Rs. = Rs. `times N=25 times 0.40`
`" "=10` Paisa
Therefore, the cost of heating is 10 paisa.