20) The total radiation from a black body per second per unit area is __________ fourth power of the absolute temperature. This statement is known as Stefan-Boltzmann law.

equal to

directly proportional to

inversely proportional to

none of these

Answer is:

directly proportional to

Explanation:

According to Stefan's law, the total radiation from a black body per second per unit area is directly proportional to the fourth power of the absolute temperature. Stefan Boltzmann law is applicable for heat transfer by radiation.

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21) In a psychrometric process, the sensible heat added is 30 kJ/s and the latent heat added is 20 kJ/s. The sensible heat factor for the process will be

0.3

0.6

0.67

1.5

Answer is:

0.6

22) The amount of radiation mainly depends upon the

nature of the body

temperature of the body

type of surface of the body

all of these

Answer is:

all of these

Explanation:

The term radiation is applied to the kinds of processes which transmit energy by means of electromagnetic waves. The amount of radiation mainly depends upon the nature of body, temperature of the body and type of surface of the body.

when the radiations are falling on a body, three things happen, i.e. a part of the radiations are absorbed by the body, a part of the radiations are reflected and the remaining radiations are transmitted through the body.