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Heat and Thermodynamics question

2023 · 30 Jan · Shift 1 · Q48

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Heat and Thermodynamics
2023 · 30 Jan · Shift 1 · Q48

Heat and Thermodynamics question

2023 · 30 Jan · Shift 1 · Q48

JEE MainPhysicsHeat and ThermodynamicsMCQ+4 / −1

Heat is given to an ideal gas in an isothermal process. A. Internal energy of the gas will decrease. B. Internal energy of the gas will increase. C. Internal energy of the gas will not change. D. The gas will do positive work. E. The gas will do negative work. Choose the correct answer from the options given below :

A
B and D only
B
C and E only
C
A and E only
D
C and D only

View written solutionFree

Correct answer: D

Key fact for an ideal gas
For an ideal gas, internal energy depends only on temperature: $U = U(T)$
Given process: isothermal
In an isothermal process, temperature remains constant: $\Delta T = 0$ Therefore, for an ideal gas, $\Delta U = 0$ So:

A. Internal energy decreases $\to$ False
B. Internal energy increases $\to$ False
C. Internal energy does not change $\to$ True

Use first law of thermodynamics
First law: $Q = \Delta U + W$ Here heat is given to the gas, so: $Q > 0$ And from isothermal ideal gas process: $\Delta U = 0$ Hence, $W = Q > 0$ So the gas does positive work.

Thus:

D. The gas will do positive work $\to$ True
E. The gas will do negative work $\to$ False

Select the correct combination
The correct statements are C and D only.

Therefore, the correct option is: $\boxed{\text{D}}$

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