6. At constant volume, temperature is increased then

1. 1. collision on walls will be less

   
   
   

   2. number of collisions per unit time will increase

   
   
   

   3. collisions will be in straight lines

   
   
   

   4. collisions will not change.

   
   
   

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1. View Hint View Answer Discuss in Forum

   As the temperature increases, the average velocity increases. So, the collisions are faster.

   Correct Option: B

   As the temperature increases, the average velocity increases. So, the collisions are faster.

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7. When volume of system is increased twice and temperature is decreased half of its initial temperature, then pressure becomes
   

1. 1. 2 times

   
   
   

   2. 4 times

   
   
   

   3. 1/2 times

   
   
   

   4. 1/4 times

   
   
   

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1. View Hint View Answer Discuss in Forum

   NA

   Correct Option: D

   NA

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8. 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 :

1. 1. 3/4

   
   
   

   2. 2

   
   
   

   3. 1/2

   
   
   

   4. 2/3

   
   
   

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1. View Hint View Answer Discuss in Forum

   From PV = nRT
   

   PA =	ρAMA	and PB =	ρBMB
   	RT		RT

   
   From question,
   

   =	PA	=	ρA		MA	= 2	MA	=	3
   	PB		ρB		MB		MB		2

   
   

   So,	MA	-	3
   	MB		4

   Correct Option: A

   From PV = nRT
   

   PA =	ρAMA	and PB =	ρBMB
   	RT		RT

   
   From question,
   

   =	PA	=	ρA		MA	= 2	MA	=	3
   	PB		ρB		MB		MB		2

   
   

   So,	MA	-	3
   	MB		4

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9. At 10° C the value of the density of a fixed mass of an ideal gas divided by its pressure is x. At 110°C this ratio is:

1. 1. X

   
   
   

   2. 383	x
      283

   
   
   

   3. 10	x
      110

   
   
   

   4. 283	x
      383

   
   
   

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1. View Hint View Answer Discuss in Forum

   Let the mass of the gas be m.
   At a fixed temperature and pressure, volume is fixed.
   

   Density of the gas, ρ =	m
   	V

   
   

   Now	ρ	=	m	=	m
   	P		PV		nRT

   
   

   ⇒	m	= x(By question)
   	nRT

   
   ⇒ xT = constant ⇒ x₁T₁ = x₂T_B
   

   ⇒ x2 ⇒	x1T1	=	283	x
   	T2		383

   
   

   	∴
   	T1	=	283K
   	T2	=	383K

   Correct Option: D

   Let the mass of the gas be m.
   At a fixed temperature and pressure, volume is fixed.
   

   Density of the gas, ρ =	m
   	V

   
   

   Now	ρ	=	m	=	m
   	P		PV		nRT

   
   

   ⇒	m	= x(By question)
   	nRT

   
   ⇒ xT = constant ⇒ x₁T₁ = x₂T_B
   

   ⇒ x2 ⇒	x1T1	=	283	x
   	T2		383

   
   

   	∴
   	T1	=	283K
   	T2	=	383K

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10. If C_s be the velocity of sound in air and C be the r.m.s velocity, then

1. 1. C_s < C

   
   
   

   2. C_s = C

   
   
   

   3. C_s = C (γ/3)^1/2

   
   
   

   4. none of these

   
   
   

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1. View Hint View Answer Discuss in Forum

   Velocity of sound (C_S) = √γP/ρ
   R.M.S. velocity of gas molecules = √3P/ρ
   

   	CS	√	γP	×	ρ	= √	γ
   	C		ρ		3P		3

   
   

   ⇒ Cs = C × √	γ
   	3

   Correct Option: C

   Velocity of sound (C_S) = √γP/ρ
   R.M.S. velocity of gas molecules = √3P/ρ
   

   	CS	√	γP	×	ρ	= √	γ
   	C		ρ		3P		3

   
   

   ⇒ Cs = C × √	γ
   	3

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