Thermal Properties of Matter

The temperature of the black body increases from T to 2T. The factor by which the rate of emission will increase, is?

• 4

• 2

• 16

• 8

Two rods of same material have same length and area. The heat ΔQ flows through them for 12 minutes when they are joint side by side. If now both the rods are joined in parallel, then the same amount of heat ΔQ will flow in :

• 24 min

• 3 min

• 12 min

• 6 min

Which of the following circular rods, (given radius r and length l) each made of the same material and whose ends are maintained at the same temperature will conduct most heat?

• r = 2r_o, l = 2l_o

• r = 2r_o, l = l_o

• r = r_o, l = l_o

• r = r_o, l = l_o

The temperature of inversion of a thermocouple is 620°C and the neutral temperature is 300^oC, what is the temperature of cold junction?

• 20^o C

• 320^o C

• -20^o C

• 40^o C

Mercury boils at 367^oC. However, mercury thermometers are made such that they can measure temperature upto 500^oC. This is done by

• maintaining vacuum above mercury column in the stem of the thermometer

• filling nitrogen gas at high pressure above the mercury column

• filling oxygen gas at high pressure above the mercury column

• filling nitrogen gas at low pressure above the mercury column

Which of the following circular rods, (given radius r and length l) each made of the same material and whose ends are maintained at the same temperature will conduct most heat?

• r = 2r_o ; l = 2 l_o

• r = 2r_o ; l = l_o

• r = r_o ; l = l_o

• r = r_o ; l = l_o

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

• $\sqrt{2} \mathrm{K}$

• 3 K

• $\frac{4}{3} \mathrm{K}$

• $\frac{2}{3}\mathrm{K}$

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

• $\frac{2\mathrm{\lambda }}{3}$

• $\frac{3\mathrm{\lambda }}{2}$

• $\frac{4\mathrm{\lambda }}{9}$

• $\frac{9\mathrm{\lambda }}{4}$

The temperature of the sun can be found out by using

• Wien's displacement law

• Kepler's law of motion

• Stefan's Boltzmann law

• Planck's law

The thermo emf of a hypothetical thermocouple varies with the temperature θ of hot junction as  E = $\mathrm{a} \mathrm{\theta } + \mathrm{b} {\mathrm{\theta }}^2$ in volts, where the ratio $\frac{\mathrm{a}}{\mathrm{b}}$ is 700^o C. If the cold junction is kept at 0^o C, then the neutral temperature is

• 700^o C 

• 1400^o C

• 390^o C

• no neutral temperature is possible for this thermocouple