Thermal Properties of Matter · Question 3

Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R). In the light of the above statements, choose the correct answer from the options given below.

1. A is true but R is false.
2. A is false but R is true.
3. Both A and R are true and R is the correct explanation of A.
4. Both A and R are true but R is NOT the correct explanation of A.

Two rods one made of copper and other made of steel of same length and same cross sectional area are joined together. The thermal conductivity of copper and steel are 385 J s-1 K-1 m-1 and 50 J s-1 K-1 m-1 respectively. The free ends of copper and steel are held at 100 and 0 respectively. The temperature at the junction is, nearly :

1. 88.5
2. 12
3. 50
4. 73

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