31.

One mole of ideal monoatomic gas (γ = 5/30) is mixed with one mole of diatomic gas(γ = 7/5). What is γ for the mixture? γ denotes the ratio of specific heat at constant pressure, to that at constant volume.

• 3/2

• 23/15

• 35/23

• 35/23

If the temperature of the sun were to increase from T to 2T and its radius from R to 2R, then the ratio of the radiant energy received on earth to what it was previously will be

• 4

• 16

• 32

• 32

Which of the following statements is correct for any thermodynamic system?

• The internal energy changes in all processes.

• Internal energy and entropy are state functions.

• The change in entropy can never be zero.

• The change in entropy can never be zero.

Two thermally insulated vessels 1 and 2 are filled with air at temperatures (T₁, T₂), volume (V₁, V₂) and pressure (P₁, P₂) respectively. If the valve joining two vessels is opened, the temperature inside the vessel at equilibrium will be

• T₁ + T₂

• T₁ + T₂/2

• 
• 

A radiation of energy E falls normally on a perfectly reflecting surface. The momentum transferred to the surface is

• E/c

• 2E/c

• Ec
• Ec

The temperature of two outer surfaces of a composite slab, consisting of two materials having coefficients of thermal conductivity K and 2K and thickness x and 4x, respectively are T₂ and T₁ (T₂ > T₁). The rate of heat transfer through the slab, in a steady state is with f, equal to

• 1

• 1/2

• 2/3

• 2/3

A light ray is incident perpendicular to one face of a 90° prism and is totally internally reflected at the glass-air interface. If the angle of reflection is 45°, we conclude that the refractive index n

• n<2

• 
• 
• 

Time taken by a 836 W heater to heat one litre of water from 10°C to 40°C is

• 50 s

• 100 s

• 150 s

• 150 s

The thermo emf of a thermocouple varies with the temperature θ of the hot junction as E = a θ + bθ² in volts where the ratio a/b is 700°C. If the cold junction is kept at 0°C, then the neutral temperature is

• 700°C

• 350°C

• 1400°C

• 1400°C

A charged particle q is shot towards another charged particle Q which is fixed, with a speed v it approaches Q upto a closest distance r and then returns. If q were given a speed 2v, the closest distances of approach would be

• r

• 2r

• r/2

• r/2