HEAT ENGINES AND REFRIGERATORS
THERMODYNAMICS
Department of Physics, Faculty of Science
Jazan University, KSA
Part-7
222 PHYS
MC questions

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

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
  

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

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 %

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