Physics Times – July 2019

(a) 398 m/s (b) 520 m/s

(c) 499 m/s (d) 532m/s

9. Figure shows the variation in temperature

( )T with the amount of heat supplied (Q)

in an isobaric process corresponding to

monoatomic (M), diatomic (D) and

polyatomic (P) gas. The initial state of all the

gases are the same and the scales for the two

axes coincide. Ignoring vibrational degrees

of freedom, the lines a, b and c respectively

correspond to: [2013]

(a) P, M and D (b) M, D and P

(c) P, D and M (d) D, M and P

[OFFLINE QUESTIONS]

1. The temperature of an open room of volume

30 m^3 increases from 17 to 27 C C due to

sunshine. The atmospheric pressure in the

room remains 1 10^5 Pa. If ni and nf are the

number of molecules in the room before and

after heating, then nfni will be: [2017]

(a) 2.5 10^25 (b)  2.5 10^25

(c)  1.61 10^23 (d) 1.38 10^23

2. Cp and Cv are specific heats at constant

pressure and constant volume respectively. It

is observed that

Cp Cv a for hydrogen gas

Cp Cv b for nitrogen gas

The correct relation between a and b:

[2017]

(a) a =14b (b) a = 28b

(c)

1

14

a b (d) a=b

3. Consider an ideal gas confined in an isolated
   closed chamber. As the gas undergoes an
   adiabatic expansion the average time of
   collision between molecules increases as Vq,
   where V is the volume of the gas. The value of

q is :

v

Cp

C

 

 

 

[2015]

(a)

3 5

6



(b)

1

2



(c)

1

2



(d)

3 5

6



4. An open glass tube is immersed in mercury in
   such a way that a length of 8 cm extends above
   the mercury level. The open end of the tube is
   then closed and sealed and the tube is raised
   vertically up by additional 46 cm. What will
   be length of the air column above mercury in
   the tube now? (Atmospheric pressure = 76
   cm of Hg) [2014]
   (a) 38 cm (b) 6 cm
   (c) 16 cm (d) 22 cm


5. A thermally insulated vessel contains an ideal
   gas of molecular mass M and ratio of specific
   heats . It is moving with speed v and it’ss
   suddenly brought to rest. Assuming no heat is
   lost to the surrounding, its temperature
   increases by [2011]

(a)

( 1) 2

2

Mv K

R







(b)

2

2

M v

K

R



(c)^2

( 1)

2

Mv K

R



(d)

( 1) 2

2( 1)

Mv K

R









6. Three perfect gases at absolute temperatures
   T T 1 , and 2 T 3 are mixed. The masses of
   molecules are m m 1 , and 2 m 3 and number of
   molecules are n n 1 , 2 and n 3 respectively..
   Assuming no loss of energy, the final
   temperature of the mixture is: [2011]

(a)

9. 
   

[2013]

[OFFLINE QUESTIONS]

1. 
   

[2017]

2. 
   

[2017]

3.

[2015]

4.

[2014]

5.

[2011]

6.

[2011]

1 1 2 2 3 3

1 2 3

n T n T n T

n n n

 

 

(b)

1 1^2 2 2^2 3 3^2

1 1 2 2 3 3

n T n T n T

n T n T n T

 

 