Question:medium

Find heat given to gas to take it from A to B. (Given: $C_v = 21$ S.I. units, $P_2 = 30$ Pa, $P_1 = 21.7$ Pa, $R = 8.3$ S.I. units, $n = 10$ moles) 

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For an isochoric process, work done is zero and heat supplied only changes internal energy.
Updated On: Mar 25, 2026
  • $30$ J
  • $21$ J
  • $42$ J
  • $50$ J
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The Correct Option is B

Solution and Explanation

Step 1: Identify the nature of work done

From the P–V diagram, the process A → B occurs at constant volume.

Hence, work done during the process is zero.

W = 0


Step 2: Apply first law of thermodynamics

According to the first law:

Q = ΔU + W

Since W = 0 for an isochoric process:

Q = ΔU


Step 3: Expression for change in internal energy

For an ideal gas, change in internal energy is given by:

ΔU = (Cv / R) × (P2 − P1)V


Step 4: Substitute given values

Cv / R = 21 / 8.3
P2 − P1 = 30 − 21.7

Q = (21 / 8.3) × (30 − 21.7)


Step 5: Final calculation

Q = 21 J


Final Answer:

The heat supplied to the gas during the process is
Q = 21 J

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