A wall has two layers A and B made of different materials. The thickness of both the layers is the same. The thermal conductivity of A and B are ${\mathrm{K}}_{\mathrm{A}}$ and ${\mathrm{K}}_{\mathrm{B}}$ such that  ${\mathrm{K}}_{\mathrm{A}}$ = 3${\mathrm{K}}_{\mathrm{B}}$. The temperature across the wall is 20°C. In thermal equilibrium 

(1) The temperature difference across A = 15°C

(2) The temperature difference across A = 5°C

(3) The temperature difference across A is 10°C

(4) The rate of transfer of heat through A is more than that through B.

             
1. \(80^{\circ}\text{C}\)
2. \(85^{\circ}\text{C}\)
3. \(90^{\circ}\text{C}\)
4. \(95^{\circ}\text{C}\)

Which of the following circular rods (given radius r and length l) each made of the same material as whose ends are maintained at the same temperature will conduct most heat ?

(1) $\mathrm{r}=2{\mathrm{r}}_0 ; \mathrm{l}=2{\mathrm{l}}_0$           

(2) $\mathrm{r}=2{\mathrm{r}}_0 ; \mathrm{l}={\mathrm{l}}_0$

(3) $\mathrm{r}={\mathrm{r}}_0 ; \mathrm{l}={\mathrm{l}}_0$               

(4) $\mathrm{r}={\mathrm{r}}_0 ; \mathrm{l}=2{\mathrm{l}}_0$

It is hotter for the same distance over the top of fire than it is inside of it, mainly because

(1) Air conducts heat upwards

(2) Heat is radiated upwards

(3) Convection takes more heat upwards

(4) Convection, conduction and radiation all contribute significantly transferring heat upwards

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:

Mode of transmission of heat, in which heat is carried by the moving particles, is 
(1) Radiation           

(2) Conduction

(3) Convection         

(4) Wave motion

In heat transfer, which method is based on gravitation ?

(1) Natural convection               

(2) Conduction

(3) Radiation                             

(4) Stirring of liquids

When fluids are heated from the bottom, convection currents are produced because -

(1) Molecular motion of fluid becomes aligned

(2) Molecular collisions take place within the fluid

(3) Heated fluid becomes more dense than the cold fluid above it

(4) Heated fluid becomes less dense than the cold fluid above it