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Free Thermodynamics MCQs with Answers

714 Thermodynamics MCQs from Physics, each with the correct answer and a written explanation of why it is correct. Free and unlimited, with no account needed.

Thermal equilibrium and heat explain how temperature and energy transfer are related, while molar specific heats describe the heat required by a gas at constant volume or constant pressure. The first law connects heat supplied, work done and change in internal energy, with sign conventions kept distinct from temperature changes.

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Thermal Equilibrium and HeatMolar Specific Heat of a GasFirst Law of Thermodynamics
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714 questions · page 32 of 36

621. In a thermodynamic system, if there is no change in temperature and internal energy, then the process is called an

  • A. Isobaric process.
  • B. Adiabatic process.
  • C. Isochoric process.
  • D. Isothermal process.

Explanation: The correct answer is isothermal process. In an isothermal process, the temperature of the system remains constant.

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Correct answer: Isothermal process.

622. The direction of heat flow from one object to another is based on the difference in their

  • A. density.
  • B. temperature.
  • C. specific heat.
  • D. thermal conductivity.

Explanation: B) Temperature (Correct): Heat always flows spontaneously from an object at a higher temperature to an object at a lower temperature.

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Correct answer: temperature.

623. The given observation table is used to determine the value of mechanical equivalent of heat. The electrical energy (W) consumed will be

  • A. 5 J
  • B. 10 J
  • C. 20 J
  • D. 40 J

Explanation: The electrical energy (W) consumed can be calculated using the formula:W = V × I × tWhere: * V = Potential Difference = 5 volts * I =…

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Correct answer: 20 J

624. All of the following are precautions which should be taken into consideration while measuring the mechanical equivalent of heat by electric method EXCEPT that the

  • A. supply of voltage is steady.
  • B. heating coil should be immersed in water.
  • C. calorimeter should be placed in an insulation box.
  • D. thermometer should touch the base of the calorimeter.

Explanation: D) Thermometer should touch the base of the calorimeter: This is not a precaution; in fact, it's something to avoid.

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Correct answer: thermometer should touch the base of the calorimeter.

625. The amount of heat energy needed to raise the temperature of 1 kg of a substance through 1 K is called

  • A. specific heat
  • B. heat capacity.
  • C. heat of fusion
  • D. heat of vapourisation

Explanation: A) Specific heat: This term (also known as specific heat capacity) is defined as the amount of heat energy required to raise the…

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Correct answer: specific heat

626. The gas is at its highest temperature at point(s)

  • A. ii only.
  • B. iv only.
  • C. i and ii.
  • D. iii and v.

Explanation: Based on the ideal gas law, PV = nRT, temperature (T) is directly proportional to the product of pressure (P) and volume (V) (T ∝ PV)…

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Correct answer: iv only.

627. In an experiment of measuring the mechanical equivalent of heat, a stirrer is placed in the calorimetre filled with hot water.After some time, the exposed end of the stirrer becomes hot.The process(es) that is/ are mainly involved in the transferring of heat processes is/ areI. radiationII. convectionIII. conduction

  • A. I only.
  • B. III only
  • C. I and II.
  • D. II and III.

Explanation: Convection:The hot water in the calorimeter transfers heat to the stirrer through convection, as the warmer water rises and cooler water…

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Correct answer: II and III.

628. A student touches the metal surface of a hot calorimetre. He is likely to burn his hand. If he holds his hand in the hot air inside the calorimetre, then he will remain fine. Which of the following statements BEST describe the given condition?

  • A. Both the metal and air are poor conductor of heat.
  • B. Both the metal and air are good conductors of heat.
  • C. Metal is a good conductor, but air is a poor conductor of heat.
  • D. Air is a good conductor, but metal is a poor conductor of heat.

Explanation: The problem describes a scenario where touching the metal surface of a hot calorimeter causes a burn, but holding a hand in the hot air…

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Correct answer: Metal is a good conductor, but air is a poor conductor of heat.

629. In a process the density of gas remains constant. If the temperature is doubled, then the change in the pressure will be:

  • A. 100% increase
  • B. 200% increase
  • C. 50% decrease
  • D. 25% decrease

Explanation: In an ideal gas where the density remains constant, the relationship between pressure (P), volume (V), and temperature (T) is given by the…

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Correct answer: 100% increase

630. Which of the following changes when taken together, will result in a decrease in the pressure of an ideal gas?

  • A. Volume decreased, temperature decreased
  • B. Volume decreased, temperature increased
  • C. Volume increased, temperature decreased
  • D. Volume increased, temperature increased

Explanation: An experimental gas law that describes the relationship between pressure and volume of a confined (Boyle's Law).

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Correct answer: Volume increased, temperature decreased

631. What is the internal energy of an object?

  • A. It is the energy associated with the object's movement through space.
  • B. It is the sum of all the microscopic potential and kinetic energies of the molecules
  • C. It is the energy due to attractions between the molecules within the object.
  • D. It is the energy associated with the random movement of the molecules in the object.

Explanation: Internal energy includes energy on a microscopic scale. It is the sum of all the microscopic energies such as: translational kinetic…

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Correct answer: It is the sum of all the microscopic potential and kinetic energies of the molecules

632. An ideal heat engine has 100% efficiency only if its exhaust temperature is:

  • A. Less than input temperature
  • B. Greater than input temperature
  • C. Equal to input temperature
  • D. 0 K

Explanation: c) Equal to input temperature:This option suggests that an ideal heat engine has 100% efficiency only if its exhaust temperature is equal…

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Correct answer: 0 K

633. During each cycle, a heat engine with an efficiency of 25% takes in 800 J of energy. How much waste heat is expelled during each cycle?

  • A. 100 J
  • B. 200 J
  • C. 300 J
  • D. 400 J
  • E. 600 J

Explanation: Efficiency =( useful power out ÷ total power in) x 100 If the efficiency of the engine is 25%, then the energy that is output for useful…

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Correct answer: 600 J

634. A container is divided into two equal portions. One portion contains an ideal gas at pressure P and temperature T while the other portion is a perfect vacuum. If a hole is opened between two portions:

  • A. There will be a change in internal energy.
  • B. There will be a change in temperature.
  • C. There will be no change in internal energy.
  • D. The external pressure will increase
  • E. The external pressure will decrease.

Explanation: When the gas expands through a hole, it is free expansion, therefore the pressure is 0 and thus according to W=PV, the work done also is…

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Correct answer: There will be no change in internal energy.

635. First law of thermodynamics is based on

  • A. Law of conservation of momentum
  • B. Law of conservation of mass
  • C. Law of conservation of charge
  • D. Law of conservatlon of energy

Explanation: The first law of thermodynamics is based on the law of conservation of energy, which states that energy cannot be created or destroyed…

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Correct answer: Law of conservatlon of energy

636. The thermodynamic process during which the pressure is kept constant is called

  • A. lsochoric process
  • B. Adiabatic process
  • C. Isobaric process
  • D. Isothermal process

Explanation: An Isobaric process is a thermodynamic process taking place at constant pressure.

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Correct answer: Isobaric process

637. In isochoric process:

  • A. Pressure is kep constant
  • B. Exchange of heat is zero
  • C. Volume is kept constant
  • D. Temperature is kept constant

Explanation: In an isochoric process, also known as an isovolumetric process, the volume remains constant.

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Correct answer: Volume is kept constant

638. The 1st law of thermodynamics is the generalization of the law of conservation of:

  • A. Mass
  • B. Energy
  • C. Charge
  • D. Momentum

Explanation: The first law of thermodynamics is an extension of the conservation of energy, stating that energy cannot be created or destroyed in a…

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Correct answer: Energy

639. A refrigerator operates for a certain time, and the work done by the electrical energy during this time is W = 1000 J. What can be said about the heat delivered to the room containing the refrigerator?

  • A. The heat delivered to the room is less than 1000 J
  • B. The heat delivered to the room is equal to 1000 J
  • C. The heat delivered to the room is greater than 1000 J
  • D. No heat is delivered to the room

Explanation: The refrigerator uses electrical energy for cooling, however, since it is not ideal, efficiency will not be 100% and will create waste…

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Correct answer: The heat delivered to the room is greater than 1000 J

640. Which statement is incorrect?

  • A. In an isobaric process, △P = 0
  • B. In an isochoric process, △W = 0
  • C. In an isothermal process △T = 0
  • D. In an isothermal process, △Q = 0

Explanation: A is correct because, in an isobaric process, the pressure of the system remains constant.B is correct because, in an isochoric process…

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Correct answer: In an isothermal process, △Q = 0
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