# Thermodynamic, examples b

- Assist.Prof of Laser Physics & Photonics en Ibb University, Yemen + Jazan University, KSA
2 de Sep de 2016
1 de 6

### Thermodynamic, examples b

1. HEAT ENGINES AND REFRIGERATORS THERMODYNAMICS Department of Physics, Faculty of Science Jazan University, KSA Part-7 222 PHYS MC questions
2. Lecture 13, p 2                      l 2 1 2 1 ( )ln ( n 2 0.69) 3 ( ) ln 2 100(0.69) 16.9% 150 373(0.69) h c by h h c h V T T W V Q V T T T V Let’s put in some numbers: V2 = 2V1 n = 3/2 (monatomic gas) T2=Th = 373K (boiling water) T1=Tc = 273K (ice water) For comparison: ηcarnot = 1 – 273/373 = 26.8% 1: find the efficiency of Stirling engine with the following parameters
3. 2: In a Carnot engine 800 J of heat is absorbed from a source at 400 K and 640 J of heat is rejected to the sink. The temperature of the sink is a) 320 K b) 100 K c) 273 K d) 250 K e) 200 K 3: A refrigerator operates in a cyclic and reversible manner (Carnot cycle).The temperature inside the refrigerator is 0°C and the room temperature is 27°C. The absorbed heat from the interior of the refrigerator Q1 = 334.72x103 J . If the coefficient of performance of the refrigerator, COP= Q1/W .the magnitude of heat Q2 rejected in the room is: a) 455.8J b) 310.6 J c) 367.8J d) 340 J e) None c c h h Q T Q T  2 1 2 1 ch h c QQ Q Q T T T T   
4. 5: The efficiency of a Carnot engine is 35.0%. What is the temperature of the cold reservoir if the temperature of the hot reservoir is 500 K? A) 175 K B) 325 K C) 269 K D) 231 K
5. 6: The maximum efficiency of a heat engine that operates between temperatures of 1000 K in the firing chamber and 600 K in the exhaust chamber is most nearly (A) 33% (B) 40% (C) 60% (D) 67% (E) 100% 7: The theoretical (Carnot) efficiency of a heat engine operating between 600C and 100C is A) 16.7 % B) 20.0 % C) 42.7 % D) 57.3 % E) 83.3 % 8: A heat engine takes in 200 J of thermal energy and performs 50 J of work in each cycle. What is its efficiency? A) 500 % B) 400 % C) 25 % D) 20 % E) 12 %
6. 9: A monoatomic ideal gas is used as the working substance for the Carnot cycle shown in the figure. Processes A→B and C → D are isothermal, while B → C and D → A are adiabatic. During process A → B, there are 400 J of work done by the gas on the surroundings. How much heat is expelled by the gas during process C → D? A) 1600 J B) 800 J C) 400 J D) 200 J E) 100 J

### Notas del editor

1. Comment: You will get the best efficiency for the largest deltaT, and for the largest “compression ratio, V2/V1.