A metal bar of length \(L\) and area of cross-section \(A\) is clamped between two rigid supports. For the material of the rod, its Young’s modulus is \(Y\) and the coefficient of linear expansion is \(\alpha\). If the temperature of the rod is increased by \(\Delta t^{\circ} \mathrm{C}\), the force exerted by the rod on the supports will be:
1. \(YAL\Delta t\)
2. \(YA\alpha\Delta t\)
3. \(\frac{YL\alpha\Delta t}{A}\)
4. \(Y\alpha AL\Delta t\)

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:

Mud houses are cooler in the summer and warmer in the winter because:

One likes to sit in the sunshine in the winter season, because:

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:

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?

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

If the sun’s surface radiates heat at $6.3\times {10}^7$ ${\mathrm{Wm}}^{-\mathrm{2 }}$then the temperature of the sun, assuming it to be a black body, will be:
$\left(\mathrm{\sigma }=5.7\times {10}^{-8}\right)$ ${\mathrm{Wm}}^{-2}{\mathrm{K}}^{-4}$
1. $5.8\times {10}^3$ $\mathrm{K}$
2. $8.5\times {10}^3$ $\mathrm{K}$
3. $3.5\times {10}^8$ $\mathrm{K}$
4. $5.3\times {10}^8$ $\mathrm{K}$