A certain quantity of water cools from \(70^{\circ}\mathrm{C}\) to \(60^{\circ}\mathrm{C}\) in the first 5 minutes and to \(54^{\circ}\mathrm{C}\) in the next 5 minutes. 
The temperature of the surroundings will be: 

1.	\(45^{\circ}\mathrm{C}\)	2.	\(20^{\circ}\mathrm{C}\)
3.	\(42^{\circ}\mathrm{C}\)	4.	\(10^{\circ}\mathrm{C}\)

The temperature of a wire of length \(1~\text{m}\) and an area of cross-section \(1~\text{cm}^2\) is increased from \(0^{\circ} \text {C}\) to \(100^{\circ} \text {C}.\) If the rod is not allowed to increase in length, the force required will be:
\((\alpha = 10^{-5}/ ^{\circ} \text {C} ~\text{and} ~Y = 10^{11} ~\text{N/m}^2)\)

A metal bar of length \(L\) and area of cross-section \(A\) is clamped between two rigid supports. For the material of the rod, it's Young’s modulus is \(Y\) and the coefficient of linear expansion is \(\alpha.\) If the temperature of the rod is increased by \(\Delta t^{\circ} \text{C},\) 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:

Two identical plates of different metals are joined to form a single plate whose thickness is double the thickness of each plate. If the coefficients of conductivity of each plate are \(2\) and \(3\) respectively, then the conductivity of the composite plate will be:
1. \(5\)
2. \(2.4\)
3. \(1.5\)                 
4. \(1.2\)

The mud houses are cooler in the summer and warmer in the winter because:

The temperature of the hot and cold ends of a 20 cm long rod in a thermal steady state is at \(100^{\circ}\mathrm{C}\) and \(20^{\circ}\mathrm{C}\) respectively. The temperature at the centre of the rod will be:
1. \(50^{\circ}\mathrm{C}\)
2. \(60^{\circ}\mathrm{C}\)
3. \(40^{\circ}\mathrm{C}\)
4. \(30^{\circ}\mathrm{C}\)

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: