The sun delivers roughly 1kwm2 of power to the earth’s surface. a parabolic mirror with a 1.5 m radius is used to focus this energy onto a beaker containing 2 l of water. estimate the time taken by the mirror to rise the temperature of water by 60°c, assuming cp, m= 75291 j k mol and ignoring energy losses to the surroundings.

Explanation:

The amount of heat required by water to increase its temperature by ,

                       q = .............. (1)    

where,       q = heat gained  

                 m= mass in kg,

                  c = specific heat (in terms of )                                                          

                dT = increase in temperature

Now, putting the given values into equation ( 1) as follows.

                 q =

                     =

                    = 4517.46 kJ

Now,  surface area of the mirror, A =

where,            r = radius of the mirror

                         = 1.5 m

Therefore,     area =  

                              =

                              = 7.065

As, 1 means = 1 kJ per second per square meter surface area.                  (as 1 W = 1 J/s)

Hence, amount of energy focused by mirror = incidence rate of solar energy x surface area of mirror

                    =

                   = 3.14 kJ s-1

Therefore, the mirror focuses 3.14 kJ energy per second

Time required by the mirror to focus 4517.46 kJ  energy =

                          = 1438.68 seconds

or,                     =

                         = 23.97 min

Thus, we can conclude that the time taken by the mirror to rise the temperature of water is 23.97 min.

zfoods? ok, pressure is used to keep the heat inside and to keep the food perfect.