At a place, the solar energy incident in one second is 640 J, on an area of one square metre. Assuming that all the solar energy is absorbed by 10 kg water, incident on its surface of area 400 `cm^(2)`. How much time will it take to raise its temperature by `70^(@)C`? (specific heat capacity of water is 4.2 J `g^(-1) .^(@)C^(-1)`)

Explanation

(i) Total energy = (Energy incident per unit area)
(x total area) x (total time)
Q = `msDeltatheta`
(ii) Find the change in temperature.
Find the mass of water and its surface area over which light is made to be incident from the given data.
Convert surface area in S.I system.
Find the solar energy incident in one second per square metre?
Find the amount of heat energy (Q) required to raise the temperature of water from formula `Q = msDeltaQ` (1)
Find the amount of solar energy incident in one second on water surface.
Is it equal to `(640 xx 0.04)`? (2)
Then find the time taken to produce Q amount of heat by solar energy which can be found out by dividing (1) by (2).
(iii) 31.9 hour