Thermal Properties of Matter · Question 8

The unit of thermal conductivity is :

1. J m-1 K-1
2. W m K-1
3. J m K-1
4. W m-1 K-1

The power radiated by a black body is P and it radiates maximum energy at wavelength, 0. If the temperature of the black body is now changed so that it radiates maximum energy at wavelength 34 0, the power radiated by it becomes nP. The value of n is

1. 34
2. 43
3. 25681
4. 81256

Two rods A and B of different materials are welded together as shown in figure. Their thermal conductivities are K1 and K2. The thermal conductivity of the composite will be [figure]

1. 3(K1 + K2)2
2. K1 + K2
3. 2 (K1 + K2)
4. K1 + K22

A spherical black body with a radius of 12 cm radiates 450 watt power at 500 K. If the radius were halved and the temperature doubled, the power radiated in watt would be

1. 450
2. 1000
3. 1800
4. 225

Coefficient of linear expansion of brass and steel rods are 1 and 2. Lengths of brass and steel rods are l1 and l2 respectively. If (l2 - l1) is maintained same at all temperatures, which one of the following relations holds good?

1. 12 l2 = 22 l1
2. 1 l1 = 2 l2
3. 1 l2 = 2 l1
4. 1 l22 = 2 l12

A piece of ice falls from a height h so that it melts completely. Only one-quarter of the heat produced is absorbed by the ice and all energy of ice gets converted into heat during its fall. The value of h [Latent heat of ice is 3.4 105 J/kg and g = 10 N/kg]

1. 136 km
2. 68 km
3. 34 km
4. 544 km

A black body is at a temperature of 5760 K. The energy of radiation emitted by the body at wavelength 250 nm is U1, at wavelength 500 nm is U2 and that at 1000 nm is U3. Wien's constant, b = 2.88 106 nm K. Which of the following is correct?

1. U1 > U2
2. U2 > U1
3. U1 = 0
4. U3 = 0

Two identical bodies are made of a material for which the heat capacity increases with temperature. One of these is at 100 , while the other one is at 0 . If the two bodies are brought into contact, then, assuming no heat loss, the final common temperature is

1. 50
2. more than 50
3. less than 50 but greater than 0
4. 0

A body cools from a temperature 3T to 2T in 10 minutes. The room temperature is T. Assume that Newton's law of cooling is applicable. The temperature of the body at the end of next 10 minutes will be

1. 74 T
2. 32 T
3. 43 T
4. T

The value of coefficient of volume expansion of glycerin is 5 10-4 K-1. The fractional change in the density of glycerin for a rise of 40 C in its temperature, is

1. 0.025
2. 0.010
3. 0.015
4. 0.020