Thermal Properties of Matter · Question 22

A piece of iron is heated in a flame. It first becomes dull red then becomes reddish yellow and finally turns to white hot. The correct explanation for the above observation is possible by using

1. Kirchhoff's Law
2. Newton's Law of cooling
3. Stefan's Law
4. Wien's displacement Law

Two metal rods 1 and 2 of same lengths have same temperature difference between their ends. Their thermal conductivities are K1 and K2 and cross sectional areas A1 and A2, respectively. If the rate of heat conduction in 1 is four times that in 2, then

1. K1A1 = 4K2A2
2. K1A1 = 2K2A2
3. 4K1A1 = K2A2
4. K1A1 = K2A2

The density of water at 20 is 998 kg/m3 and at 40 is 992 kg/m3. The coefficient of volume expansion of water is

1. 3 10-4/
2. 2 10-4/
3. 6 10-4/
4. 10 10-4/

A slab of stone of area 0.36 m2 and thickness 0.1 m is exposed on the lower surface to steam at 100 . A block of ice at 0 rests on the upper surface of the slab. In one hour 4.8 kg of ice is melted. The thermal conductivity of slab is (Given latent heat of fusion of ice = 3.36 105 J kg-1)

1. 1.24 J/m/s/ C
2. 1.29 J/m/s/ C
3. 2.05 J/m/s/ C
4. 1.02 J/m/s/ C

If the radius of a star is R and it acts as a black body, what would be the temperature of the star, in which the rate of energy production is Q?

1. Q4 2
2. ( Q4 2 )-1/2
3. ( 4 2Q )1/4
4. ( Q4 2 )1/4

Liquid oxygen at 50 K is heated to 300 K at constant pressure of 1 atm. The rate of heating is constant. Which one of the following graphs represents the variation of temperature with time ?

1. [figure]
2. [figure]
3. [figure]
4. [figure]

A cylindrical metallic rod in thermal contact with two reservoirs of heat at its two ends conducts an amount of heat Q in time t. The metallic rod is melted and the material is formed into a rod of half the radius of the original rod. What is the amount of heat conducted by the new rod, when placed in thermal contact with the two reservoirs in time t?

1. Q4
2. Q16
3. 2Q
4. Q2

The total radiant energy per unit area, normal to the direction of incidence, received at a distance R from the centre of a star of radius r, whose outer surface radiates as a black body at a temperature T K is given by

1. 2T4R2
2. 2T44 2
3. 2T4R4
4. 4 2T4R2

Assuming the sun to have a spherical outer surface of radius r, radiating like a black body at temperature t C, the power received by a unit surface, (normal to the incident rays) at a distance R from the centre of the sun is where is the Stefan's constant.

1. r2 (t + 273)44 2
2. 16 2r2 4R2
3. r2 (t + 273)4R2
4. 4 2 4R2

A black body at 227 C radiates heat at the rate of 7 cal/cm2 s. At a temperature of 727 C, the rate of heat radiated in the same units will be

1. 50
2. 112
3. 80
4. 60