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

Initially a beaker has 100 g of water at temperature 90°C. Later another 600 g of water at temperature 20°C was poured into the beaker. The temperature, T of the water after mixing is

• 20°C

• 30°C

• 45°C

• 55°C

A metallic bar of coefficient of linear expansion 10^-5 K^-1 is heated from 0°C to 100°C. The percentage increase in its length is

• 0.1 % 

• 1 % 

• 10 %

• 0.01 %

Two perfectly black spheres A and B having radii 8 cm and 2 cm are maintained at temperatures 127°C and 527°C, respectively. The ratio of the energy radiated by A to that by B is

• 1 : 2

• 1 : 1

• 2 : 1

• 1 : 4

Hot water in a vessel kept in a room cools from 70°C to 65°C in t₁ minutes, from 65°C to 60°C in t₂ minutes and from 60°C to 55°C in t₃ minutes then,

• t₁ < t₂ > t₃

• t₁ = t₂ = t₃

• t₁ < t₂ < t₃

• t₁ < t₂ = t₃

29.

If the time taken by a hot body to cool from 50°C to 40°C is 10 min when the surrounding temperature is 25°C, then the time taken for it to cool from 40°C to 30°C when the surrounding temperature is 15°C, is

• 40 min

• 10 min

• 5 min

• 15 min

1 cc of water becomes 1681 cc of steam when boiled at a pressure of10⁵ Nm^-2. The increasing internal energy of the system is (Latent heat of steam is 540 cal g^-1 , 1 cal = 4.2 J)

• 300 cal

• 500 cal

• 225 cal

• 600 cal