The mud houses are cooler in the summer and warmer in the winter because:
1. | The mud is a superconductor of heat. |
2. | The mud is a good conductor of heat. |
3. | The mud is a bad conductor of heat. |
4. | None of the above. |
One likes to sit in the sunshine in the winter season, because:
1. | the air around the body is hot, and the body absorbs heat from it. |
2. | we get energy from the sun. |
3. | we get heat by conduction from the sun. |
4. | none of the above |
Air is a bad conductor of heat or partly conducts heat. Still, a vacuum is to be placed between the walls of the thermos flask because:
1. | it is difficult to fill the air between the walls of the thermos flask. |
2. | due to more pressure of air, the thermos can get cracks. |
3. | by convection, heat can flow through the air. |
4. | on filling the air, there is no advantage. |
While measuring the thermal conductivity of a liquid, we keep the upper part hot and the lower part cool, so that:
1. | convection may be stopped |
2. | radiation may be stopped |
3. | heat conduction is easier downwards |
4. | it is easier and more convenient to do so |
On a clear sunny day, an object at temperature \(T\) is placed on the top of a high mountain. An identical object at the same temperature is placed at the foot of the mountain. If both the objects are exposed to sun-rays for two hours in an identical manner, the object placed on the top of a mountain will register a temperature:
1. | higher than the object at the foot. |
2. | lower than the object at the foot. |
3. | equal to the object at the foot. |
4. | none of the above. |
Taking into account the radiation that a human body emits which of the following statements is true?
1. | The radiation is emitted only during the day. |
2. | The radiation is emitted during the summers and absorbed during the winters. |
3. | The radiation emitted lies in the ultraviolet region and hence is not visible. |
4. | The radiation emitted is in the infra-red region. |
A black body has a maximum wavelength at a temperature of \(2000~\text K.\) Its corresponding wavelength at temperatures of \(3000~\text K\) will be:
1. | \(\dfrac{3}{2} \lambda_m\) | 2. | \(\dfrac{2}{3} \lambda_m\) |
3. | \(\dfrac{4}{9} \lambda_m\) | 4. | \(\dfrac{9}{4} \lambda_m\) |
If the sun’s surface radiates heat at \(6.3\times 10^{7}~\text{Wm}^{-2}\) then the temperature of the sun, assuming it to be a black body, will be:
\(\left(\sigma = 5.7\times 10^{-8}~\text{Wm}^{-2}\text{K}^{-4}\right)\)
1. \(5.8\times 10^{3}~\text{K}\)
2. \(8.5\times 10^{3}~\text{K}\)
3. \(3.5\times 10^{8}~\text{K}\)
4. \(5.3\times 10^{8}~\text{K}\)
A block of metal is heated to a temperature much higher than the room temperature and allowed to cool in a room free from air currents. Which of the following curves correctly represents the rate of cooling?
1. | 2. | ||
3. | 4. |
When two ends of a rod wrapped with cotton are maintained at different temperatures and, after some time, every point of the rod attains a constant temperature, then:
1. | conduction of heat at different points of the rod stops because the temperature is not increasing |
2. | the rod is a bad conductor of heat |
3. | the heat is being radiated from each point of the rod |
4. | each point of the rod is giving heat to its neighbour at the same rate at which it is receiving heat |