CBSE Class 11 Transfer of Heat Worksheet B

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1. Why is the energy of thermal radiation less than that of visible light? 

2. Two rods A and B are of equal length. Each rod has its ends at temperature T₁ and T₂ (T₁ > T₂). What is the condition that will ensure equal rates of flow through the rods A and B?

3. A Sphere is at a temperature of 6oo k. Its cooling rate is R in an external environment of 200k. If temperature falls to 400k. What is the cooling rate R₁ in terms of R?

4. If the temperature of the sun is doubled, the rate of energy received on each will increases by what factor?

5. How do you explain the emission of long - wavelength by the object at low temperature?

6. If the radiation from the moon gives maxima at λ = 4700 A⁰ and λ = 14x10^-6m. What conclusion can be drawn from the above information?

7. Differentiate between conduction, convection and radiation?

8. The tile floor feels colder than the wooden floor even though both floor materials are at same temperature. Why?

9. A spherical black body of radius 12cm radiates 450w power at 500k. If the radius were halved and the temperature doubled, what would be the power radiated?

10. A cylinder of radius R made of a material of thermal conductivity K₁ is surrounded by a cylindrical shell of inner radius R and other radius 2R made of material of thermal conductivity K₂. The 2 ends of combined system are maintained at two different temperatures. There is no loss of heat across the clinical surface and the system is in steady state calculate the effective thermal conductivity of the  system?

11. A room has a 4m x 4m x10cm concrete roof (K1 = 1.26w|m|°C). At some instant, the temperature outside is 46°c and radius 32°c.

1) Calculate amount of heat flowing per second into the room through the roof.

2) If bricks (K₂ – 0.56w |m|°c) of thickness 7.5cm are laid down on roof, calculate the new rate of heat flow under the same temperature conditions?

12. A bar of copper of length 75cm and a bar of length 125cm are joined end to end. Both are of circular cross – section with diameters 2cm. The free ends of copper and steel are maintained at 100°c and 0°c respectively. The surfaces of the bars are thermally insulated. What is the temperature of copper – steel junction? Thermal conductivity of copper = 9.2x10^-2k cal |m|0c|s and that of steel is 1.1x10^-2 k cal|m|°c|s? 

Click on link below to download CBSE Class 11 Transfer of Heat Worksheet B.