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:
1. | conduction of heat at different points of the rod stops because the temperature is not increasing |
2. | the rod is a bad conductor of heat |
3. | the heat is being radiated from each point of the rod |
4. | each point of the rod is giving heat to its neighbour at the same rate at which it is receiving heat |
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
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
1. | Very high thermal conductivity and helps in further ice formation |
2. | Very low conductivity and retards further formation of ice |
3. | It permits quick convection and retards further formation of ice |
4. | It is very good radiator |
Wires A and B have identical lengths and have circular cross-sections. The radius of A is twice the radius of B i.e. . For a given temperature difference between the two ends, both wires conduct heat at the same rate. The relation between the thermal conductivities is given by
(1)
(2)
(3)
(4)