Question

$∆U$ is equal to:

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

Answer 1

The correct option is A

Adiabatic work

Explanation of correct option:

Option (A)-Adiabatic work

First Law of Thermodynamics:

1. According to the first law of thermodynamics, “Energy can neither be transferred nor be created, it just transforms from one system to another”.
2. Mathematically, it can be expressed as $∆U=Q+W$.
3. Adiabatic system: In this system, there is no transfer of heat, that is the heat value is zero, $Q=0$.
4. So the equation is given as, $∆U=0+W=W$. Thus, energy is equal to work in an adiabatic system.
5. Therefore, the energy change is equal to adiabatic work.

Explanation of incorrect options:

Option (B): Isothermal system:

1. In this system, there is no change in temperature.
2. Therefore, the change in energy is also equal to zero $∆U=0$.
3. Thus, change in energy is not equal to isothermal work.

Option (C): Isochoric system:

1. In this system, there is no change in volume.
2. Since $W=-pdv=0$, $∆U=Q+W=Q$.
3. Thus, change in energy is not equal to isobaric work.

Option (D): Isobaric system:

1. In this system, there is no change in pressure
2. . Since $W=-pdv$, $∆U=Q+W=Q-pdv$.
3. Thus, change in energy is not equal to isobaric work.

Hence, the correct option is option A.