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:

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:

Taking into account the radiation that a human body emits which of the following statements is true?

According to Wein's law:
1. ${\mathrm{\lambda }}_{\mathrm{m}}\mathrm{T}$= constant                 

2. $\frac{{\mathrm{\lambda }}_{\mathrm{m}}}{\mathrm{T}}$= constant

3. $\frac{T}{{\mathrm{\lambda }}_{\mathrm{m}}}$= constant                 

4. $\mathrm{T}+{\mathrm{\lambda }}_{\mathrm{m}}$= constant

A black body at \(200\) K is found to emit maximum energy at a wavelength of \(14\) \(\mu \)m. When its temperature is raised to \(1000\) K, the wavelength at which maximum energy is emitted will be:

If the temperature of the sun becomes twice its present temperature, then:

A black body has a maximum wavelength at a temperature of 2000 K. Its corresponding wavelength at temperatures of 3000 K will be: 

The temperature of an object is \(400^{\circ}\mathrm{C}\)$\mathrm{}$. The temperature of the surroundings may be assumed to be negligible. What temperature would cause the energy to radiate twice as quickly? (Given, \(2^{\frac{1}{4}} \approx 1.18\))
1. \(200^{\circ}\mathrm{C}\)
2. 200 K
3. \(800^{\circ}\mathrm{C}\)$\mathrm{}$         
4. 800 K

If the temperature of the body is increased from \(-73^{\circ}\mathrm{C}\)$\mathrm{}$ to \(327^{\circ}\mathrm{C}\)$\mathrm{}$, then the ratio of energy emitted per second in both cases is:
1. 1 : 3                         
2. 1 : 81
3. 1 : 27                       
4. 1 : 9