CBSE Class 11-science Physics Transfer of Heat by Radiation

• a body cools from 90°c to 70°c in 5minutes. temperature of surrounding is 30°c. its temperature after next 10 min is
• the unit of thermal conductivity is
  
•   The temperature of perfect black body changes from 3000K to 4000K.What is the percentage change in energy radiation.
• The temperature of perfect black body changes from 3000K to 4000K.What is the percentage change in energy radiation.
• A furnace emits radiation at 2000 K. Treating it as black body radiation, calculate Wave length at which emission is maximum and the corresponding radiant flux density
•  A furnace emits radiation at 2000 K. Treating it as a black body radiation, calculate the monochromatic radiant flux density at 1 micron m wavelength
• There are two thin spheres A and B of the same material and same thickness.They emit like black bodies.Radius of A is double that of B.A and B have same tempt. T .When A and B are kept in a room of tempt T0(less than T),the ratio of their rates of cooling (rate of fall of tempt) is
• Two bodies A and B have emissivities 0.5 and 0.8 respec .At some tempt the two bodies have emissive powers at these tempt.
• Explain the working of room heater. How can we increase the efficiency of convections in radiator of a room heater?
• By what mode of heat transfer is mercury heated?

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