Kinetic Theory of Gases · JEE Main previous year questions

2020 4 questions

1. Q402020 · 6 Sept 2020 · Shift 1

   Molecules of an ideal gas are known to have three translational degrees of freedom and two rotational degrees of freedom. The gas is maintained at a temperature of T. The total internal energy, U of a mole of this gas, and the value of $\gamma \left(=\frac{C_p}{C_v}\right)$ are given, respectively by:

   1. A.$U=\frac{5}{2}RT$ and $\gamma =\frac{7}{5}$
   2. B.$U=5RT$ and $\gamma =\frac{6}{5}$
   3. C.$U=5RT$ and $\gamma =\frac{7}{5}$
   4. D.$U=\frac{5}{2}RT$ and $\gamma =\frac{6}{5}$
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   Answer: A

2. Q362020 · 3 Sept 2020 · Shift 2

   To raise the temperature of a certain mass of gas by $50^{\circ }\mathrm{C}$ at a constant pressure, 160 calories of heat is required. When the same mass of gas is cooled by $100^{\circ }\mathrm{C}$ at constant volume, 240 calories of heat is released. How many degrees of freedom does each molecule of this gas have (assume gas to be ideal)?

   1. A.6
   2. B.7
   3. C.5
   4. D.3
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   Answer: A

3. Q292020 · 2 Sept 2020 · Shift 2

   An ideal gas in a closed container is slowly heated. As its temperature increases, which of the following statements are true? (A) the mean free path of the molecules decreases. (B) the mean collision time between the molecules decreases. (C) the mean free path remains unchanged. (D) the mean collision time remains unchanged.

   1. A.(C) and (D)
   2. B.(A) and (D)
   3. C.(B) and (C)
   4. D.(A) and (B)
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   Answer: C

4. Q322020 · 7 Jan 2020 · Shift 1

   Two moles of an ideal gas with $\frac{C_p}{C_v}=\frac{5}{3}$ are mixed with 3 moles of another ideal gas with $\frac{C_p}{C_v}=\frac{4}{3}$. The value of $\frac{C_p}{C_v}$ for the mixture is :

   1. A.1.50
   2. B.1.45
   3. C.1.47
   4. D.1.42
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   Answer: D