Under steady state, the temperature of a body 

(1) Increases with time

(2) Decreases with time

(3) Does not change with time and is same at all the points of the body

(4) Does not change with time but is different at different points of the body

The coefficient of thermal conductivity depends upon

(1) Temperature difference of two surfaces

(2) Area of the plate

(3) Thickness of the plate

(4) Material of the plate

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:

The ratio of thermal conductivity of two rods of different material is 5 : 4. The two rods of same area of cross-section and same thermal resistance will have the lengths in the ratio 

(1) 4 : 5             

(2) 9 : 1

(3) 1 : 9             

(4) 5 : 4

In variable state, the rate of flow of heat is controlled by
(1) Density of material               

(2) Specific heat

(3) Thermal conductivity             

(4) All the above factors

The dimensions of thermal resistance are
(1) ${\mathrm{M}}^{-1}{\mathrm{L}}^{-2}{\mathrm{T}}^3\mathrm{K}$           

(2) ${\mathrm{ML}}^2{\mathrm{T}}^{-2}{\mathrm{K}}^{-1}$

(3) ${\mathrm{ML}}^2{\mathrm{T}}^{-3}\mathrm{K}$               

(4) ${\mathrm{ML}}^2{\mathrm{T}}^{-2}{\mathrm{K}}^{-2}$

A slab consists of two parallel layers of copper and brass of the same thickness and having thermal conductivities in the ratio 1 : 4. If the free face of brass is at 100°C and that of copper at 0°C, the temperature of interface is
1. 80°C               

2. 20°C

3. 60°C               

4. 40°C

Two thin blankets keep more hotness than one blanket of thickness equal to these two. The reason is

(1) Their surface area increases

(2) A layer of air is formed between these two blankets, which is bad conductor

(3) These have more wool

(4) They absorb more heat from outside

Ice formed over lakes has