A room illuminated by an extended source. The iluminance at a particular portion of a wal can be increased by
A room illuminated by an extended source. The iluminance at a particular portion of a wal can be increased by
A
moving the source
B
rotating the source
C
bringing some mirrors in proper positions
D
changing the colour of the source
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A, B, C, D
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The efficiency of a heat engine is defined as the ratio of the mechanical work done by the engine in one cycle to the heat absorbed from the high temperature source . eta = (W)/(Q_(1)) = (Q_(1) - Q_(2))/(Q_(1)) Cornot devised an ideal engine which is based on a reversible cycle of four operations in succession: isothermal expansion , adiabatic expansion. isothermal compression and adiabatic compression. For carnot cycle (Q_(1))/(T_(1)) = (Q_(2))/(T_(2)) . Thus eta = (Q_(1) - Q_(2))/(Q_(1)) = (T_(1) - T_(2))/(T_(1)) According to carnot theorem "No irreversible engine can have efficiency greater than carnot reversible engine working between same hot and cold reservoirs". A carnot engine whose low temperature reservoir is at 7^(@)C has an efficiency of 50% . It is desired to increase the efficiency to 70% . By how many degrees should the temperature of the high temperature reservoir be increased?
Refrigerator is an apparatus which takes heat from a cold body, work is done on it and the work done together with the heat absorbed is rejected to the source. An ideal refrigerator can be regarded as Carnot's ideal heat engine working in the reverse direction. The coefficient of performance of refrigerator is defined as beta = ("Heat extracted from cold reservoir")/("work done on working substance") = (Q_(2))/(W) = (Q_(2))/(Q_(1)- Q_(2)) = (T_(2))/(T_(1) - T_(2)) A Carnot's refrigerator takes heat from water at 0^(@)C and discards it to a room temperature at 27^(@)C . 1 Kg of water at 0^(@)C is to be changed into ice at 0^(@)C. (L_(ice) = 80"kcal//kg") How many calories of heat are discarded to the room?
Refrigerator is an apparatus which takes heat from a cold body, work is done on it and the work done together with the heat absorbed is rejected to the source. An ideal refrigerator can be regarded as Carnot's ideal heat engine working in the reverse direction. The coefficient of performance of refrigerator is defined as beta = ("Heat extracted from cold reservoir")/("work done on working substance") = (Q_(2))/(W) = (Q_(2))/(Q_(1)- Q_(2)) = (T_(2))/(T_(1) - T_(2)) A Carnot's refrigerator takes heat from water at 0^(@)C and discards it to a room temperature at 27^(@)C . 1 Kg of water at 0^(@)C is to be changed into ice at 0^(@)C. (L_(ice) = 80"kcal//kg") What is the coefficient of performance of the machine?
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