Mechanical Engineering - Thermodynamics - Discussion

Option B is correct.

In isothermal process temperature kept constant. And internal energy function of temperature only.

An isothermal process is a change of a system, in which the temperature remains constant: ΔT = 0. This typically occurs when a system is in contact with an outside thermal reservoir (heat bath), and the change occurs slowly enough to allow the system to continually adjust to the temperature of the reservoir through heat exchange. In contrast, an adiabatic process is where a system exchanges no heat with its surroundings (Q = 0). In other words, in an isothermal process, the value ΔT = 0 but Q ≠ 0, while in an adiabatic process, ΔT ≠ 0 but Q = 0.

Internal energy always zero in isothermal process. Formula.

du=Cv*dt.

Internal energy is function of temperature.

So no change in internal energy.

In fact the answer is wrong.

The phase change process is isothermal but the internal energy varies.

This answer is only correct for ideal gases. The question needs to clarify this.

Then how 100 celsius. Water changes to 100 degree vapour? Please clarify?

Internal energy is the function of temperature so, temperature is the constants until internal energy is the constants.

delta U = MC delta T.

Internal energy directly depends on temperature.