Free First Law of Thermodynamics MCQs with Answers

• A. 8.4%.
• B. 15.3%.
• C. 18.3%.
• D. 84.5%.

Explanation: The efficiency of a turbine in a thermal power plant can be calculated using the Carnot efficiency formula, which is the maximum…

• A. mass of active substance.
• B. volume of active substance.
• C. pressure on the hot reservoir.
• D. temperature of hot and cold reservoirs.

Explanation: The efficiency of a Carnot cycle, which is a theoretical thermodynamic cycle, is solely dependent on the absolute temperatures of the hot…

• A. Adiabatic compression  isothermal expansion  isobaric compression  isochoric expansion
• B. Isothermal expansion  isobaric compression  adiabatic compression  isochoric expansion
• C. Isothermal expansion  adiabatic expansion  isothermal compression  adiabatic compression
• D. Isobaric compression  isothermal expansion  isochoric expansion  adiabatic compression

Explanation: 1. Isothermal expansion: Heat is absorbed at a constant high temperature (\(T_{H}\)) while the system expands and does work. 2.

• A. 25 %
• B. 50 %
• C. 60 %
• D. 65 %

Explanation: Efficiency (η) = 1 - (T_cold / T_hot)Where: * T_hot = Temperature of the fire chamber (hot reservoir) = 1500 K * T_cold = Temperature of…

• A. i to ii
• B. ii to iii
• C. iii to iv
• D. iv to v

Explanation: 1. Understanding Work Done in a P-V Graph: In a Pressure-Volume (P-V) graph, the work done by or on a gas during a process is represented…

• 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…

• 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…

• 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…

• 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…

• 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…

• 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.

• 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.

• 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…

• 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…

• 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…

• A. Temperature remains constant
• B. Pressure remains constant
• C. Volume remains constant
• D. There is no transfer of heat

Explanation: In an adiabatic process, there is no transfer of heat between the system and the surroundings i.e.

• A. Hot reservoir is at 0K
• B. Hot reservoir is at 0C
• C. Cold reservoir is at 0C
• D. Cold reservoir is at 0 Kelvin

Explanation: Cold reservoir at 0K: This is the only option that could theoretically allow for an ideal reversible heat engine to be 100% efficient.

• A. 70J
• B. 150J
• C. 190J
• D. 180J

Explanation: Since heat is being added, so work is being done by system. ΔU = Heat supplied - Work done by the system= 110 - 40 = 70J

• A. No heat is added to or taken out of a system
• B. No change of temperature takes place
• C. Boyle's law is applicable
• D. Pressure and volume remains constant

Explanation: In an adiabatic process, no energy is added to or removed from the system in the form of heat.

• A. Slow compression of a gas into a cylinder
• B. Changes due to friction
• C. Explosion
• D. Dissipation of energy

Explanation: The correct answer is Option A: Slow compression of a gas into a cylinder.