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   The surface area of a concentrator type solar heater is 5m2. It can reflect 80% of solar radiation incident on it while it absorbs the rest. Calculate the energy concentrated by the heater at its focus in 2 hours if solar energy was delivered to it at the rate of .

Answer:

                  It is advantageous to convert bio-mass into a bio-gas rather than burning bio-mass directly because of the following reasons (i) Heating capacity of bio-gas is more than that of bio-mass. (ii) Bio-gas produces lesser pollution as compared to bio-mass.                               (1+1)                 The vegetation which is submerged, rots in anaerobic condition and gives out large amount of methane in nature which is a greenhouse gas.                                            (2)