The temperature, at which centigrade and Fahrenheit scales give the same reading, is

• - 40°

• 40°

• - 30°

• 30°

A brass rod of length 500 mm and diameter 3 mm is joined to a steel rod of same length and diameter at 50°C. If the coefficients of linear expansion of brass and steel are 2.5 x 10^-5 ° C^-1 and 1.25 x 10^-5 ° C^-1 , then change in length of the combined rod at 200°C is

• 2.4 mm

• 2.8 mm

• 3.2 mm

• 3.6 mm

A copper block of mass 4 kg is heated in a furnance to a temperature 425°C and then placed on a large ice block. The mass of ice that will melt in this process will be (Specific heat of copper = 500 J kg^-1 ° C^-1 and heat of fusion of ice = 336 kJ kg^-1 )

• 0.5 kg

• 1 kg

• 1.5 kg

• 2.5 kg

A block of ice at - 10°C is slowly heated and converted to steam at 100°C. Which of the following curves represents this phenomenon qualitatively ?

In which mode of transmission, the heat waves travel along straight line with the speed of light?

• thermal radiation

• forced convection

• natural convection

• thermal conduction

Consider a compound slab consisting of two, different materials having equal lengths, thicknesses and thermal conductivities K and  2 K respectively. The equivalent thermal conductivity of the slab is

• $\sqrt{2} \mathrm{K}$

• 3 K

• $\frac{4}{3} \mathrm{K}$

• $\frac{2}{3} \mathrm{K}$

An ideal black body at room temperature is thrown into a furnance. It is observed that

• it is the darkest body at all times

• it cannot be distinguished at all times

• initially it is the darkest body and later it becomes brightest

• initially it is the darkest body and later it cannot be distinguished

If temperature of the sun were to increase from T to 2 T and its radius from R to 2R, then how many times the radiant energy will be received on the earth ?

• 4

• 16

• 32

• 64

A black body has a wavelength of λ at temperature 2000 K. Its corresponding wavelength at temperature 3000 K will be

• $\frac{2\mathrm{\lambda }}{3}$

• $\frac{3\mathrm{\lambda }}{2}$

• $\frac{4\mathrm{\lambda }}{9}$

• $\frac{9\mathrm{\lambda }}{4}$

An ice box made of Styrofoam (Thermal conductivity = 0.01Jm^-1 s^-1 K^-1 ) is used to keep liquids cool. It has a total wall area including lid of 0.8 m and wall thickness of 2.0 cm. A bottle of water is placed in the box and filled with ice. If the outside temperature is 30°C the rate of flow of heat into the box is (in J-s^-1 )

• 16

• 14

• 12

• 10