Two ends of a rod of a non-uniform area of cross-section are maintained at temperatures T₁ and T₂ (T₁>T₂) as shown in the figure.

If l is heat current through the cross-section of conductor at a distance x from its left face, then the variation of l with x is best represented by:

1. 

2. 

3. 

4. 

Four rods of the same material with different radii \(r\) and length \(l\) are used to connect two reservoirs of heat at different temperatures. Which one will conduct maximum heat?
1. \(r=1~\text{cm}, l= 1~\text{m}\)
2. \(r=2~\text{cm}, l= 2~\text{m}\)
3. \(r=1~\text{cm}, l= \frac{1}{2}~\text{m}\)
4. \(r=2~\text{cm}, l= \frac{1}{2}~\text{m}\)

Four rods of the same material and having the same cross-sectional area and length have been joined as shown. The temperature of the junction of four rods will be:

1. 20°C

2. 30°C

3. 45°C

4. 60°C

Why it is hotter for the same distance over the top of a candle than it is inside of its flame?

1. Conduction of heat in the air is upward.

2. Heat is maximum radiated in the upward direction.

3. Radiation and conduction both contribute to transferring heat upwards.

4. Convection takes more heat in the upward direction.

In gravity-free space, heat transfer is not possible by:

1. Conduction

2. Convection

3. Radiation

4. Both (1) and (3)

Which factor does not affect convection?

1. Temperature difference

2. The rate of movement of carrying medium

3. The volumetric specific heat of carrying medium

4. The thermal conductivity of carrying medium

A polished plate with a rough black spot is heated to a high temperature and then taken to a dark room, then,

1. Spot will appear brighter than the plate.

2. Spot will appear darker than the plate.

3. Both will appear equally brighter.

4. Both will not be visible.

Select the incorrect statement.

1. A body radiates at all temperatures except 0 K.

2. A good reflector is a bad radiator.

3. A colder body can radiate heat to the hotter surroundings.

4. A body does not radiate when its temperature is below 0°C.

"A good absorber is a good emitter" is explained by:

1. Stefan's law

2. Wien's law

3. Newton's law of cooling

4. Kirchhoff's law

The rate of radiation of energy from a hot object is maximum if its surface is:

1. White and smooth

2. Black and rough

3. Black and smooth

4. White and rough