Physics · Thermodynamics · chapter 11 of 14

Class 11 Physics Chapter 11: Thermodynamics Assertion-reason questions with answers

2 assertion-reason questions on Thermodynamics, each with its answer and the reason, written from the NCERT chapter. For school exams on the CBSE pattern, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): When an ideal gas expands isothermally, the heat it absorbs equals the work it does. Reason (R): The internal energy of an ideal gas depends only on its temperature.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both are true. Since U of an ideal gas depends only on T, ΔU = 0 at constant temperature, and the First Law gives Q = W. R is exactly the reason for A.

Question 2
Assertion (A): The calorie is defined for the rise in temperature of 1 g of water from 14.5 °C to 15.5 °C. Reason (R): In SI units the specific heat capacity of water is 4186 J kg⁻¹ K⁻¹.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Both are true. The interval is specified because the specific heat of water varies slightly with temperature; the SI value of the specific heat does not explain why a particular interval is chosen.

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