Thermodynamics
Q. What happens to the internal energy of an ideal gas when it is compressed adiabatically?
A.
It increases
B.
It decreases
C.
It remains constant
D.
It depends on the initial temperature
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Solution
In an adiabatic compression, work is done on the gas, which increases its internal energy.
Correct Answer: A — It increases
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Q. What happens to the pressure of an ideal gas if its volume is halved while keeping the temperature constant?
A.
Pressure remains the same
B.
Pressure doubles
C.
Pressure halves
D.
Pressure quadruples
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Solution
According to Boyle's law, for a given amount of gas at constant temperature, pressure is inversely proportional to volume. Halving the volume doubles the pressure.
Correct Answer: B — Pressure doubles
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Q. What happens to the rate of heat transfer through a material if its thickness is increased?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Depends on the material
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Solution
The rate of heat transfer decreases with an increase in thickness, as per Fourier's Law.
Correct Answer: B — Decreases
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Q. What happens to the temperature of a gas when it expands adiabatically?
A.
It increases
B.
It decreases
C.
It remains constant
D.
It depends on the gas
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Solution
During adiabatic expansion, a gas does work on its surroundings, which results in a decrease in temperature.
Correct Answer: B — It decreases
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Q. What happens to the temperature of a substance during a phase change?
A.
It increases
B.
It decreases
C.
It remains constant
D.
It fluctuates
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Solution
During a phase change, the temperature of a substance remains constant while heat is added or removed.
Correct Answer: C — It remains constant
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Q. What happens to the thermal energy of a substance when it undergoes a phase change?
A.
It increases
B.
It decreases
C.
It remains constant
D.
It becomes zero
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Solution
During a phase change, the thermal energy remains constant as the energy is used to change the state rather than increase the temperature.
Correct Answer: C — It remains constant
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Q. What is the change in internal energy (ΔU) for an ideal gas in an isochoric process?
A.
ΔU = Q
B.
ΔU = W
C.
ΔU = 0
D.
ΔU = Q - W
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Solution
In an isochoric process, the change in internal energy is equal to the heat added to the system, ΔU = Q.
Correct Answer: A — ΔU = Q
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Q. What is the change in internal energy for an ideal gas during an isochoric process?
A.
Zero
B.
nRΔT
C.
Q
D.
W
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Solution
In an isochoric process, the change in internal energy is equal to the heat added to the system, ΔU = Q.
Correct Answer: C — Q
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Q. What is the change in internal energy for an ideal gas undergoing an isochoric process?
A.
Zero
B.
Equal to the heat added
C.
Equal to the work done
D.
Equal to the change in temperature
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Solution
In an isochoric process, the volume remains constant, and the change in internal energy is equal to the heat added to the system.
Correct Answer: B — Equal to the heat added
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Q. What is the change in internal energy of an ideal gas during an isochoric process?
A.
Increases
B.
Decreases
C.
Remains constant
D.
Depends on the amount of gas
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Solution
In an isochoric process, the volume remains constant, and any heat added to the system increases the internal energy of the gas.
Correct Answer: A — Increases
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Q. What is the effect of increasing the surface area of an object on its rate of heat transfer?
A.
Increases
B.
Decreases
C.
No effect
D.
Depends on the material
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Solution
Increasing the surface area of an object increases the rate of heat transfer, as more area is available for heat exchange.
Correct Answer: A — Increases
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Q. What is the effect of increasing the surface area of an object on its rate of heat transfer by radiation?
A.
Decreases
B.
Increases
C.
Remains constant
D.
Becomes zero
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Solution
Increasing the surface area of an object increases the rate of heat transfer by radiation, as more surface is available for emitting energy.
Correct Answer: B — Increases
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Q. What is the effect of increasing the temperature of a gas at constant volume?
A.
Pressure decreases
B.
Pressure increases
C.
Volume increases
D.
Density increases
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Solution
Increasing the temperature of a gas at constant volume results in an increase in pressure, according to Gay-Lussac's law.
Correct Answer: B — Pressure increases
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Q. What is the efficiency of a Carnot engine operating between temperatures T1 and T2?
A.
(T1 - T2) / T1
B.
T2 / T1
C.
(T1 - T2) / T2
D.
1 - (T2 / T1)
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Solution
The efficiency of a Carnot engine is given by the formula: efficiency = 1 - (T2 / T1), where T1 is the higher temperature and T2 is the lower temperature.
Correct Answer: D — 1 - (T2 / T1)
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Q. What is the entropy change for a reversible isothermal expansion of an ideal gas?
A.
nR ln(Vf/Vi)
B.
0
C.
nR(Tf - Ti)
D.
nC ln(Vf/Vi)
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Solution
The entropy change for a reversible isothermal expansion of an ideal gas is ΔS = nR ln(Vf/Vi).
Correct Answer: A — nR ln(Vf/Vi)
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Q. What is the entropy change for a reversible isothermal process?
A.
Zero
B.
nR ln(Vf/Vi)
C.
nR(Tf - Ti)
D.
nR ln(Tf/Ti)
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Solution
The entropy change for a reversible isothermal process is ΔS = nR ln(Vf/Vi).
Correct Answer: B — nR ln(Vf/Vi)
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Q. What is the entropy change for a reversible process?
A.
Always positive
B.
Always negative
C.
Can be zero
D.
Depends on the path taken
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Solution
For a reversible process, the entropy change can be zero if the process is isothermal and reversible.
Correct Answer: C — Can be zero
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Q. What is the final temperature when 200 g of water at 90°C is mixed with 300 g of water at 30°C?
A.
50°C
B.
60°C
C.
70°C
D.
80°C
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Solution
Using the formula m1*T1 + m2*T2 = (m1 + m2)*Tf, we find Tf = (200*90 + 300*30) / (200 + 300) = 70°C.
Correct Answer: C — 70°C
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Q. What is the first law of thermodynamics?
A.
Energy cannot be created or destroyed
B.
Entropy of an isolated system always increases
C.
Heat cannot spontaneously flow from a colder body to a hotter body
D.
The total energy of a system is constant
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Solution
The first law of thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another.
Correct Answer: A — Energy cannot be created or destroyed
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Q. What is the heat required to raise the temperature of 250 g of aluminum from 25°C to 75°C? (Specific heat of aluminum = 0.9 J/g°C)
A.
4500 J
B.
5000 J
C.
6000 J
D.
7000 J
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Solution
Q = m*c*ΔT = 250 g * 0.9 J/g°C * (75°C - 25°C) = 4500 J.
Correct Answer: A — 4500 J
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Q. What is the latent heat of fusion for ice?
A.
334 J/g
B.
2260 J/g
C.
4190 J/g
D.
1000 J/g
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Solution
The latent heat of fusion for ice is approximately 334 J/g.
Correct Answer: A — 334 J/g
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Q. What is the latent heat of fusion?
A.
Heat required to change a solid to a liquid
B.
Heat required to change a liquid to a gas
C.
Heat required to change a gas to a solid
D.
Heat required to change a liquid to a solid
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Solution
Latent heat of fusion is the heat required to change a solid into a liquid at its melting point.
Correct Answer: A — Heat required to change a solid to a liquid
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Q. What is the main mechanism of heat transfer in liquids and gases?
A.
Conduction
B.
Convection
C.
Radiation
D.
Insulation
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Solution
Convection is the primary mechanism of heat transfer in liquids and gases due to the movement of the fluid.
Correct Answer: B — Convection
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Q. What is the main mechanism of heat transfer in liquids?
A.
Conduction
B.
Convection
C.
Radiation
D.
Insulation
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Solution
In liquids, convection is the main mechanism of heat transfer, as the fluid moves and carries heat with it.
Correct Answer: B — Convection
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Q. What is the mode of heat transfer that occurs through a fluid due to density differences?
A.
Conduction
B.
Convection
C.
Radiation
D.
Insulation
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Solution
Convection is the mode of heat transfer that occurs through a fluid due to density differences.
Correct Answer: B — Convection
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Q. What is the mode of heat transfer that occurs through a fluid without any movement of the fluid itself?
A.
Conduction
B.
Convection
C.
Radiation
D.
Diffusion
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Solution
Conduction is the mode of heat transfer that occurs through a solid or stationary fluid without any movement of the fluid itself.
Correct Answer: A — Conduction
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Q. What is the primary factor affecting the rate of heat transfer by conduction?
A.
Surface area
B.
Temperature difference
C.
Material properties
D.
All of the above
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Solution
All of the above factors affect the rate of heat transfer by conduction.
Correct Answer: D — All of the above
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Q. What is the primary mechanism of heat transfer in a vacuum?
A.
Conduction
B.
Convection
C.
Radiation
D.
None of the above
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Solution
In a vacuum, heat transfer occurs primarily through radiation, as there are no particles to conduct or convect heat.
Correct Answer: C — Radiation
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Q. What is the primary mechanism of heat transfer in liquids and gases?
A.
Conduction
B.
Convection
C.
Radiation
D.
Insulation
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Solution
In liquids and gases, convection is the primary mechanism of heat transfer, as it involves the movement of fluid.
Correct Answer: B — Convection
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Q. What is the primary mechanism of heat transfer in liquids?
A.
Conduction
B.
Convection
C.
Radiation
D.
All of the above
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Solution
In liquids, convection is the primary mechanism of heat transfer, although conduction and radiation can also occur.
Correct Answer: B — Convection
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