NEET Previous Year Questions (2014-2024): Kinetic Theory | Physics Class 11 PDF Download

2023

Q1: The temperature of a gas is –50°C. To what temperature the gas should be heated so that the rms speed is increased by 3 times?     [2023]
(a) 669°C 
(b) 3295°C
(c) 3097 K
(d) 223 K
Ans: (b)  3295°C

Explanation:

The root mean square (RMS) speed v_rms of a gas is given by the equation:

T₁ = 273− 50
= 223 K
v_rms is increased by 3 times
T₂ = ?
So, final rms speed = v + 3v = 4v

2021

Q1: Match column - I and column - II and choose the correct match from the given choices.     [2021]

(a) (A) - (Q), (B) - (P), (C) - (S), (D) - (R)
(b) (A) - (R), (B) - (Q), (C) - (P), (D) - (S)
(c) (A) - (R), (B) - (P), (C) - (S), (D) - (Q)
(d) (A) - (Q), (B) - (R), (C) - (S), (D) - (P)
Ans: (a) (A) - (Q), (B) - (P), (C) - (S), (D) - (R)

Explanation:

2020

Q1: A cylinder contains hydrogen gas at pressure of 249 kPa and temperature 27°C.
Its density is : (R = 8.3 J mol^-1 K^-1) [2020]
(a) 0.1 kg/m³ 
(b) 0.02 kg/m³ 
(c) 0.5 kg/m³ 
(d) 0.2 kg/m³
Ans: (d) 0.2 kg/m³

Explanation:

Using the ideal gas equation, we have

∴ PV = nRT

Q2: The mean free path for a gas, with molecular diameter d and number density n can be expressed as :     [2020]
(a)

(b) 

(c)

(d)

Ans: (d)

Explanation:

The mean free path for gas is given by

Q3: The average thermal energy for a mono-atomic gas is (k_B is Boltzmann constant and T, absolute temperature) [2020]
(a) 1/2k_BT
(b) 3/2k_BT
(c) 5/2k_BT
(d) 7/2k_BT
Ans: (b) 3/2kBT

Explanation:

2019

Q1: Increase in temperature of a gas filled in a container would lead to:    [2019]
(a) Increase in its mass
(b) Increase in its kinetic energy
(c) Decrease in its pressure
(d) Decrease in intermolecular distance
Ans: (b)  Increase in its kinetic energy

2018

Q1: At what temperature will the rms speed of oxygen molecules become just sufficient for escaping from the Earth's atmosphere ? (Given: Mass of oxygen molecule (m) = 2.76 × 10^–26 kg Boltzmann's constant kB = 1.38 × 10^–23 J K^–1):-    [2018]
(a) 2.508 × 10⁴ K
(b) 8.360 × 10⁴ K
(c) 5.016 × 10⁴ K
(d) 1.254 × 10⁴ K
Ans: (b) 8.360 × 10⁴ K

Explanation:

2017

Q1: The de-Broglie wavelength of a neutron in thermal equilibrium with heavy water at a temperature T(Kelvin) and mass m, is:-    [2017]
(a)
(b)
(c)
(d)
Ans: (a)

Explanation:

Q2: A gas mixture consists of 2 moles of O₂ and 4 moles of Ar at temperature T. Neglecting all vibrational modes, the total internal energy of the system is:- [2017]
(a) 15 RT
(b) 9 RT
(c) 11 RT
(d) 4 RT
Ans: (c)

Explanation:

2016

Q1: The molecules of a given mass of a gas have r.m.s. velocity of 200 ms^-1 at 27°C and 1.0 x 10^-5 Nm^-2 pressure. When the temperature and pressure of the gas are respectively, 127°C and 0.05 x 10⁵Nm², the r.m.s. velocity of velocity of its molecules in ms^-1 is; [2016]
(a) 100 / 3
(b) 100 √2
(c) 400 / √3
(d) 100√2 / 3
Ans:

Explanation:

Q2: A given sample of an ideal gas occupies a volume V at a pressure P and absolute temperature T.  The mass of each molecule of the gas is m. Which of the following gives the density of the gas ?       [2016]
(a) P/(kT)
(b) Pm/(kT)
(c) P/(kTV)
(d) mkT
Ans: (b)  Pm/(kT)

Explanation:
We know that ideal gas equation is
PV = NkT
Where, P is the pressure
V is the volume
N is the number of molecules
k is the Boltzmann constant
T is the temperature

2015

Q1: The ratio of the specific heats  in terms of degrees of freedom (n) is given by: [2015]
(a)
(b)
(c)
(d)
Ans:

Explanation:

Q2: Two vessels separately contain two ideal gases A and B at the same temperature, the pressure of A being twice that of B. Under such conditions, the density of A is found to be 1.5 times the density of B. The ratio of molecular weight of A and B is  [2015]
(a) 2
(b) 1/2
(c) 2/3
(d) 3/4 
Ans: (d) 3/4

Explanation:
According to an ideal gas equation, the molecular weight of an ideal gas is
M = ρRT / P 

where P, T and r are the pressure, temperature and density of the gas respectively and R is the universal gas constant.
∴ The molecular weight of A is

 and that of B is

Hence, their corresponding ratio is 

2014

Q1: The mean free path of molecules of a gas,(radius ‘r’) is inversely proportional to:    [2014] 
(a) r
(b) √r
(c) r³
(d) r²
Ans: (d) r²

Explanation: