The thermal conductivity of a rod depends on

1.  length

2.  mass

3.  area of cross section

4.  material of the rod.

In a room containing air, heat can go from one place to another:

A solid at temperature T₁, is kept in an evacuated chamber at temperature T₂ > T₁ . The rate of increase of temperature of the body is proportional to

1. T₂ – T₁

2.   \(T^2_2 -T^2_1\)n

3.   \(T^3_2 -T^3_1\)

4.   \(T^4_2 -T^4_1\)

The thermal radiation emitted by a body is proportional to Tⁿ where T is its absolute temperature. The value of n is exactly 4 for

1.  a blackbody

2.  all bodies

3.  bodies painted black only

4.  polished bodies only.

Two bodies A and B having equal surface areas are maintained at temperatures 10°C and 20°C. The thermal radiation emitted in a given time by A and B are in the ratio

1.   1 : 1.15

2.  1 : 2

3.   1 : 4

4.  1 : 16.

One end of a metal rod is kept in a furnace. In steady state, the temperature of the rod

1.  increases

2.  decreases

3.  remains constant

4.  is nonuniform

Newton’s law of cooling is a special case of

1.  Wien’s displacement law

2.  Kirchoff 's law

3.  Stefan’s law

4.  Planck’s law.

            
1. a

2. b

3. c

4. d

A hot liquid is kept in a big room. The logarithm of the numerical value of the temperature difference between the liquid and the room is plotted against time. The plot will be very nearly

1.   a straight line

2.   a circular arc

3.   a parabola

4.   an ellipse.

A body cools down from \(65^\circ \text{C}\) to \(60^\circ \text{C}\) in \(5\) minutes. It will cool down from \(60^\circ \text{C}\) to \(55^\circ \text{C}\) in: