Embibe Experts Solutions for Chapter: Heat Transfer, Exercise 2: Exercise-2

Assertion : Heat radiations and light have identical properties.

Reason : A cool body does not radiate heat to the hotter surroundings.

Assertion : Coldness is felt in summer when we enter in air-conditioned room.

Reason : At every possible temperature, there is a continuous heat energy exchange between a body and its surrounding.

Assertion: IBB (Ideal Black Body) is a good emitter at high temperature.

Reason: Good emitters are good absorbers and vice versa.

Assertion: Absorptive power is a dimensionless quantity and a body having low emissive power should have low absorptive power.

Reason: The ratio of emissive power to absorptive power is same for all bodies at a given temperature and is equal to the emissive power of a black body at that temperature.

Assertion: A body that is a good radiator is also a good absorber of radiation at a given wavelength.

Reason: According to Kirchhoff's law the absorptivity of a body is equal to its emissivity at a given wavelength.

Assertion: Bodies radiate heat at all temperatures.

Reason: The rate of radiation of heat is inversely proportional to the fourth power of absolute temperature.

Assertion: If the temperature of a star is doubled, then the rate of loss of heat from it become $16$ times.

Reason: Specific heat varies with temperature under the above condition of the star.

Assertion: The radiation from the sun's surface varies as the fourth power of its absolute temperature.

Reason: The sun is not a black body.