In a room containing air, heat can go from one place to another:
1. by conduction only
2. by convection only
3. by radiation only
4. by all three modes

A solid at temperature \(T_1\), is kept in an evacuated chamber at temperature \(T_2>T_1\). The rate of increase of temperature of the body is proportional to:
1. \(T_2-T_1\)
2. \(T^2_2 -T^2_1 \)
3. \(T^3_2 -T^3_1\) 
4. \(T^4_2 -T^4_1\)

A rod \(\mathrm{A}\) has a coefficient of thermal expansion \((\alpha_A)\) which is twice of that of rod \(\mathrm{B}\) \((\alpha_B)\). The two rods have length \(l_A,~l_B\) where \(l_A=2l_B\). If the two rods were joined end-to-end, the average coefficient of thermal expansion is:

The ice-point reading on a thermometer scale is found to be \(20^\circ,\) while the steam point is found to be \(70^\circ.\) When this thermometer reads \(100^\circ ,\) the actual temperature is:
1. \(80^\circ\text{C}\)
2. \(130^\circ\text{C}\)
3. \(160^\circ\text{C}\)
4. \(200^\circ\text{C}\)

The temperature at which the Celsius and Fahrenheit thermometers agree (to give the same numerical value) is:

Two rods of identical dimensions are joined end-to-end, and the ends of the composite rod are kept at \(0^\circ\text{C}\) and \(100^\circ\text{C}\) (as shown in the diagram). The temperature of the joint is found to be \(40^\circ\text{C}.\) Assuming no loss of heat through the sides of the rods, the ratio of the conductivities of the rods \(\dfrac{K_1}{K_2}\) is:

The temperature of water at the surface of a deep lake is \(2^{\circ} ~\text{C}.\) The temperature expected at the bottom is:
1. \(0^{\circ} \mathrm{C}\)
2. \(2^{\circ} \mathrm{C}\)
3. \(4^{\circ} \mathrm{C}\)
4. \(6^{\circ} \mathrm{C}\)