# NCERT Class 11 Physics Chapter 13 Kinetic Theory CBSE Board Sample Problems

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## MCQ I

**Question 1:**

A cubic vessel (with faces horizontal vertical) contains an ideal gas at NTP. The vessel is being carried by a rocket which is moving at a speed of in vertical direction. The pressure of the gas inside the vessel as observed by us on the ground

(a) Remains the same because is very much smaller than vrms of the gas.

(b) Remains the same because motion of the vessel as a whole does not affect the relative motion of the gas molecules and the walls.

(c) Will increase by a factor equal to *v* where was the original mean square velocity of the gas.

(d) Will be different on the top wall and bottom wall of the vessel.

**Answer: (b)**

Comment for discussion: This brings in concepts of relative motion and that when collision takes place; it is the relative velocity which changes.

**Question 2:**

1 mole of an ideal gas is contained in a cubical volume *V*, ABCDEFGH at (Fig. 13.1). One face of the cube (EFGH) is made up of a material which totally absorbs any incident on it. At any given time,

(a) The pressure on EFGH would be zero.

(b) The pressure on all the faces will the equal.

(c) The pressure of EFGH would be double the pressure on ABCD.

(d) The pressure on EFGH would be half that on ABCD. gas molecule

**Answer: (d)**

Comment for discussion: In the ideal case that we normally consider, each collision transfers twice the magnitude of its normal momentum. On the face EFGH, it transfers only half of that.

**Question 3:**

Boyle’s law is applicable for an

(a) Adiabatic process.

(b) Isothermal process.

(c) Isobaric process.

(d) Isochoric process.

**Answer: (b)**

**Question 4:**

A cylinder containing an ideal gas is in vertical position and has a piston of mass *M* that is able to move up or down without friction (Fig. 13.2). If the temperature is increased,

(a) Both *p* and *V* of the gas will change.

(b) Only *p* will increase according to Charle’s law.

(c) *V* will change but not *p.*

(d) *p* will change but not *V*.

**Answer: (c)**

This is a constant pressure arrangement.

**Question 5:**

Fig. 13.3

(a)

(b)

(c)

(d) Data is insufficient.

**Answer: (a)**

**Question 6:**

mole of gas is contained in a box of volume at . The gas is heated to a temperature of and the gas gets converted to a gas of hydrogen atoms. The final pressure would be (considering all gases to be ideal)

(a) Same as the pressure initially.

(b) 2 times the pressure initially.

(c) 10 times the pressure initially.

(d) 20 times the pressure initially.

**Answer: (d)**

Comment for discussion: The usual statement for the perfect gas law somehow emphasizes molecules. If a gas exists in atomic form (perfectly possible) or a combination of atomic and molecular form, the law is not clearly stated.

**Question 7:**

A vessel of volume *V* contains a mixture of mole of Hydrogen and mole of Oxygen (both considered as ideal). Let denote the fraction of molecules with speed between *v* and with similarly for oxygen. Then

(a) obeys the Maxwell’s distribution law.

(b) will obey the Maxwell’s distribution law separately.

(c) Neither *,* nor will obey the Maxwell’s distribution law.

(d) and will be the same.

**Answer: (b)**

Comment: In a mixture, the average kinetic energy are equating.

Hence, distribution in velocity are quite different.

**Question 8:**

An inflated rubber balloon contains one mole of an ideal gas, has a pressure *p*, volume *V* and temperature *T*. If the temperature rises to 1.1 *T*, and the volume is increaset to 1.05 V, the final pressure will be

(a)

(b)

(c) Less than *p*

(d) Between *p* and 1.1.

**Answer: (d)**

Comment for discussion: In this chapter, one has discussed constant pressure and constant volume situations but in real life there are many situations where both change. If the surfaces were rigid, would rise to . However, as the pressure rises, also rises such that finally is 1.1 with . Hence(d).