“Absorption, Reflection and Transmission of Heat” MHT-CET Class 12 Physics Crash Course | Chapter Kinetic theory of Gases and Radiation
In this session G.S. Khairnar discussed the theory and MCQ’s of “Absorption, Reflection and Transmission of Heat”. The session will be useful for all the aspirants of MHT-CET 2022. The session will be in Marathi and English.
Absorption, Reflection and Transmission of Heat:-
Dear students we all know that, every substance shows different behaviour when subjected to heat. When heat is given to substance, internal kinetic energy of substance changes at higher extent and substance gains the energy termed as internal energy. According to the molecular structure of substance, some substances are very good conductor of heat whereas some are poor conductors. Some substances have ability to store heat and some transmit it to the neighbouring substance or surrounding.
In this article we are going to discuss the possible ways of distribution of heat when incident on substance.
Let’s discuss Absorption, reflection and transmission of heat ….!
Consider object in the shape of cube and heat ‘Q’ is incident on the substance as shown in fig. below.
The heat incident on the substance can be divided into three parts (depending on the surface on which it is incident). The substance can reflect heat, can absorb or can transmit the heat incident on ot.
But according to law of conservation of energy, the total heat incident on the substance is always same as the total parts of heat that are divided into other forms.
To explain the heat absorbed, reflected and transmitted by substance let us define some important terms.
Coefficient of absorption (a): The coefficient of absorption of a body is the ratio of quantity of radiant heat absorbed by the body to the total quantity of radiant heat incident on it.
i.e. a = Qa / Q
Coefficient of reflection (r): The coefficient of reflection of a body is the ratio of quantity of heat reflected from the surface of the body to the total amount of heat incident on the surface of body.”
i.e. r = Qr / Q
Coefficient of transmission (t): The coefficient of transmission of a body is the ratio of quantity of radiant heat that transmitted through the body to the total quantity of radiant heat incident on it.
i.e. t = Qt / Q
Relation between a, r, t:
- If for the given body t=0 and (r + a) = 1 then that body is called athermanous body, i.e. the body which do not allowed to transmit the heat radiations is called athermanous body. e.g. water, wood, iron, copper, lampblack, water vapour.
- The body which allows transmitting the heat radiations through it is called diathermanous body. e.g. glass, quartz, sodium chloride, hydrogen, oxygen, dry air, rock salts. These substances are neither good absorbers nor good reflectors.
Absorption, Reflection and Transmission of Heat:-
Let’s solve following MCQ’s……………….!
Q.1) When heat is incident on athermanous substance,
a) t≠0
b) t=0
c) t<0>1
d) t≥0>1
Answer
a) t≠0
Q.2) Substance which does not transmit the heat through it is called as…..
a) bad conductors of heat
b) bad transmitters of heat
c) diathaemanous material
d) athermanous material
Answer
c) diathaemanous material
Q.3) Dark colours are usually considered as …..
a) good reflectors of heat
b) good absorbers of heat
c) poor transmitters of heat
d) poor absorbers of heat
Answer
b) good absorbers of heat
Q.4) 4000 J of heat is incident on diathermanous substance of coefficient of absorption 0.36. The amount of heat absorbed and heat reflected by the substance is …..
a) 1440 J,2560 J
b) 2560 J,1440 J
c) 1440 J,4000 J
d) 2560 J,4000 J
Answer
a) 1440 J,2560 J
Q.5) Coefficient of absorption of the material which absorbs 64% of heat incident on it is….
a) 0.16
b) 0.32
c) 0.48
d) 0.64
Answer
d) 0.64
Q.6) When heat incident on the substance, which of the following is correct?
a) a + r+ t=1
b) a + r=1
c) a + r + t≠1
d) a + r=0
Answer
a) a + r+ t=1
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