MDCAT Thermodynamics 2021-22

If P is the pressure, U is the internal energy and dV the volume increase of system, then by definition

• dU = dQ + PdV

• dU = dQ + VdP

• dU = dQ – PdV

• dU = dQ – VdP

In a thermodynamic system, if  represents the increase in internal energy and the work done by the system. Which of the following statements is true

If an ideal gas is isothermally expanded, its internal energy will

• Remain the same

• Increase

• Decrease or increase depending on the nature of the gas

• Decrease

If the internal energy of a gas decreases by an amount equal to the external work, the gas is under going

• Adiabatic expansion

• Adiabatic compression

•  Isothermal expansion

• Isochoric expansion

A refrigerator is

• Heat engine

• An electric motor

• Air cooler

•                                  Heat engine working in backward direction

A system X is neither in thermal equilibrium with Y nor with Z. The system Y and Z

• Must be in thermal equilibrium

• Can not be in thermal equilibrium

• May be in thermal equilibrium

• None of these

Theoretically the efficiency of a Carnot engine is 100% when the temperature of the sink is

• 0^oF

• 0^oC

• 0^oK

• 0^oR

An ideal heat engine exhausting heat at 27^oC is to have 25% efficiency. It must take heat at

• 127^oC

• 227^oC

• 327^oC

• 673^oC

If heat is removed from a body, the change in entropy is

• Positive

• Negative

• Remain constant

• None of these