Heat Engines, Second Law and Entropy MCQs

Question 1

600 J flows from a body at 600 K to one at 300 K. The total entropy change is:

Accepted Answer

+1 J/K

Answer

+3 J/K

Answer

0 J/K

Answer

-1 J/K

Question 2

A refrigerator removes 900 J from its contents using 300 J of electrical work. The heat given out to the kitchen is:

Accepted Answer

1200 J

Answer

300 J

Answer

900 J

Answer

600 J

Question 3

The unit of entropy is:

Accepted Answer

J/K

Answer

J

Answer

K

Answer

W

Question 4

A pendulum swinging in air gradually stops; this shows the process is:

Accepted Answer

irreversible

Answer

reversible

Answer

cyclic and reversible

Answer

isothermal

Question 5

A gas expanding freely into a vacuum is:

Accepted Answer

irreversible

Answer

adiabatic and reversible

Answer

quasi-static

Answer

reversible

Question 6

A drop of ink in water spreads out because:

Accepted Answer

the spread-out state is far more probable

Answer

ink molecules repel each other strongly

Answer

the water heats the ink

Answer

ink is pushed by water

Question 7

An engine that turns all its heat into work would violate:

Accepted Answer

the second law of thermodynamics

Answer

the first law

Answer

Newton's third law

Answer

the zeroth law

Question 8

A heat engine takes in 800 J from the hot reservoir and rejects 200 J to the cold reservoir. Its efficiency is:

Accepted Answer

75%

Answer

25%

Answer

37.5%

Answer

80%

Question 9

A claim that an engine working between 400 K and 300 K has 40% efficiency is:

Accepted Answer

impossible — the maximum is 25%

Answer

below the limit

Answer

possible

Answer

exactly the Carnot value

Question 10

A heat engine takes in 1000 J from the hot reservoir and rejects 600 J to the cold reservoir. Its efficiency is:

Accepted Answer

40%

Answer

60%

Answer

62.5%

Answer

20%

Question 11

Ice cubes in a warm drink melt rather than grow because:

Accepted Answer

this increases the total entropy

Answer

it decreases entropy

Answer

of gravity

Answer

energy is destroyed

Question 12

The SI unit of entropy is:

Accepted Answer

J K^-1

Answer

K J^-1

Answer

J

Answer

J s

Question 13

Which factor makes a process irreversible?

Accepted Answer

friction

Answer

slow change

Answer

no heat transfer

Answer

equilibrium at each step

Question 14

Although energy is conserved, we speak of an 'energy crisis' because:

Accepted Answer

useful energy is degraded into heat that can't easily be used

Answer

temperature is falling

Answer

the first law fails

Answer

energy is destroyed

Question 15

When food is digested, chemical energy is ultimately degraded to:

Accepted Answer

body heat lost to the surroundings

Answer

potential energy stored forever

Answer

mass

Answer

nuclear energy

Question 16

'Time's arrow' (the one-way direction of time) is linked to:

Accepted Answer

the increase of entropy

Answer

Newton's first law

Answer

the speed of light

Answer

conservation of energy

Question 17

Melting of ice at exactly 0 °C with heat supplied infinitely slowly is:

Accepted Answer

approximately reversible

Answer

explosive

Answer

impossible

Answer

highly irreversible

Question 18

In all natural (real) processes, the total entropy of the universe:

Accepted Answer

increases

Answer

stays the same

Answer

becomes zero

Answer

decreases

Question 19

When a gas expands isothermally, its entropy:

Accepted Answer

increases

Answer

becomes zero

Answer

stays constant

Answer

decreases

Question 20

The work done by a heat engine in one cycle is:

Accepted Answer

W = QH - QC

Answer

W = QH QC

Answer

W = QC - QH

Answer

W = QH + QC

Question 21

A gas has more entropy than a solid of the same substance because:

Accepted Answer

its particles have many more possible positions and speeds

Answer

it has fewer particles

Answer

it is heavier

Answer

it is colder

Question 22

The Carnot engine is important because:

Accepted Answer

no engine working between the same two temperatures can be more efficient

Answer

it is used in all cars

Answer

it has 100% efficiency

Answer

it needs no cold reservoir

Question 23

Heating a solid makes its atoms:

Accepted Answer

vibrate more randomly about their positions

Answer

line up more neatly

Answer

stop vibrating

Answer

lose mass

Question 24

The same amount of heat produces a larger increase in disorder when added to a:

Accepted Answer

cold body

Answer

hot body

Answer

body at any temperature equally

Answer

body at infinite temperature

Question 25

The maximum possible efficiency of an engine working between 127 °C and 27 °C is:

Accepted Answer

25%

Answer

78.7%

Answer

75%

Answer

50%

Heat Engines, Second Law and Entropy MCQs — Physics (page 4)

76. 600 J flows from a body at 600 K to one at 300 K. The total entropy change is:

77. A refrigerator removes 900 J from its contents using 300 J of electrical work. The heat given out to the kitchen is:

78. The unit of entropy is:

79. A pendulum swinging in air gradually stops; this shows the process is:

80. A gas expanding freely into a vacuum is:

81. A drop of ink in water spreads out because:

82. An engine that turns all its heat into work would violate:

83. A heat engine takes in 800 J from the hot reservoir and rejects 200 J to the cold reservoir. Its efficiency is:

84. A claim that an engine working between 400 K and 300 K has 40% efficiency is:

85. A heat engine takes in 1000 J from the hot reservoir and rejects 600 J to the cold reservoir. Its efficiency is:

86. Ice cubes in a warm drink melt rather than grow because:

87. The SI unit of entropy is:

88. Which factor makes a process irreversible?

89. Although energy is conserved, we speak of an 'energy crisis' because:

90. When food is digested, chemical energy is ultimately degraded to:

91. 'Time's arrow' (the one-way direction of time) is linked to:

92. Melting of ice at exactly 0 °C with heat supplied infinitely slowly is:

93. In all natural (real) processes, the total entropy of the universe:

94. When a gas expands isothermally, its entropy:

95. The work done by a heat engine in one cycle is:

96. A gas has more entropy than a solid of the same substance because:

97. The Carnot engine is important because:

98. Heating a solid makes its atoms:

99. The same amount of heat produces a larger increase in disorder when added to a:

100. The maximum possible efficiency of an engine working between 127 °C and 27 °C is:

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