Thermal Properties of Matter · Question 5

A cup of coffee cools from 90 to 80 in t minutes, when the room temperature is 20 . The time taken by a similar cup of coffee to cool from 80 to 60 at a room temperature same at 20 is :

1. 513t
2. 1310t
3. 135t
4. 1013t

The quantities of heat required to raise the temperature of two solid copper spheres of radii r1 and r2 (r1 = 1.5r2) through 1 K are in the ratio :

1. 94
2. 32
3. 53
4. 278

A copper rod of 88 cm and an aluminium rod of unknown length have their increase in length independent of increase in temperature. The length of aluminium rod is : ( Cu = 1.7 10-5 K-1 and Al = 2.2 10-5 K-1)

1. 119.9 cm
2. 88 cm
3. 68 cm
4. 6.8 cm

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