Physics Q98 – AP-EAMCET 2025

Home Physics ThermodynamicsQuestion #505

The thermodynamic process in which the change in internal energy of the system becomes zero is

Clue 1 of 3: Internal Energy and Temperature

The internal energy of an ideal gas is solely a function of its absolute temperature.

🧠 Full Solution Path

Step 1: Relate Internal Energy to Temperature✦ Active

For an ideal gas, the internal energy ( $U$ ) is directly proportional to its absolute temperature ( $T$ ). This relationship can be expressed as $U = n C_{v} T$ , where $n$ is the number of moles and $C_{v}$ is the molar specific heat at constant volume.

💡 Teacher's Secret Hint

This relationship holds true for ideal gases. For real gases, internal energy can also depend on volume and pressure, but for most introductory thermodynamics problems, the ideal gas assumption is made.

Step 2: Apply the Condition for Zero Change in Internal Energy○ Expand

The problem states that the change in internal energy of the system becomes zero, i.e., $Δ U = 0$ . Based on the relationship from Step 1, if $Δ U = 0$ , then $n C_{v} Δ T = 0$ . Since $n$ (number of moles) and $C_{v}$ (molar specific heat) are generally non-zero, it implies that the change in temperature ( $Δ T$ ) must be zero.

Step 3: Identify the Thermodynamic Process○ Expand

A thermodynamic process in which the temperature of the system remains constant ( $Δ T = 0$ ) is defined as an isothermal process.

Step 4: Evaluate the Options○ Expand

Let's review the given options:

1. **Adiabatic process:** A process where no heat is exchanged with the surroundings ( $Q = 0$ ). Temperature can change.

2. **Isothermal process:** A process where the temperature remains constant ( $Δ T = 0$ ). For an ideal gas, this means $Δ U = 0$ .

3. **Isobaric process:** A process where the pressure remains constant ( $Δ P = 0$ ). Temperature and internal energy can change.

4. **Isochoric process:** A process where the volume remains constant ( $Δ V = 0$ ). Temperature and internal energy can change.

Therefore, the isothermal process is the one in which the change in internal energy of the system becomes zero (for an ideal gas).

💡 Teacher's Secret Hint

Remember the key characteristic of each thermodynamic process: Isothermal (constant temperature), Adiabatic (no heat exchange), Isobaric (constant pressure), and Isochoric (constant volume).

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Physics Question 98 – AP-EAMCET 2025

Clue 1 of 3: Internal Energy and Temperature

🧠 Full Solution Path