XII Physics Solved Numericals | Ch# 17 Second Law of Thermodynamics

Board: Sindh Boards Class : 12, Second Year Subject: Physics Unit #17 Second Law of Thermodynamics Numericals: Numerical: 1. A Carnot engine takes 2000J of heat from a reservoir at 500K does some work, and discards some heat to a reservoir at 350K. How much heat is discarded, how much work does the engine do, and what is the efficiency? (Ans: 1400J, 600J, 30%) 2. One kilogram of ice at 0°C is melted and converted to water at 0°C. Compute its change in entropy. (Ans: 1220 J.K-1) 3. In a high-pressure steam turbine engine, the steam is heated to 600°C and exhausted at about 90°C. What is the highest possible efficiency of any engine that operates between these two temperatures? (Ans: 58.4 %) 4. Temperature difference between the surface water and bottom water in Manchester Lake might be 5°C.Assuming the surface water to be at 20°C. What highest efficiency a steam engine could have if it operates between these two temperatures? (Ans: 1.71%) 5. A heat engine works at the rate of 500kW. The efficiency of the engine is 30%. Calculate the loss of heat per hour. (Ans: 4.2 x 109J) 6. A heat engine performs work of 0.4166 watts in one hour and rejects 4500J of heat to the sink. What is the efficiency of engine? (Ans: 24.9%) 7. A Carnot engine operates between the temperatures 850K and 300K. the engine performs 1200J of work in each cycle, which takes 0.25 sec (a) What is the efficiency of this engine? (b) What is the average power of this engine? (c) How much energy is extracted as heat from the high temperature reservoir? (d) How much energy is delivered as heat to the low temperature reservoir? [Ans (a) 65% (b) 4.8KW (c) 1855J (d) 655J1 8. A Carnot engine absorbs 52kJ as heat and exhaust 36kJ as heat in each cycle. Calculate: (a) The engine efficiency (b) The work done per cycle in kilojoules. [Ans (a) 30.76% (b) 16KJ)