Question

In a closed room, heat transfer takes place by:
A. Conduction
B. Convection
C. Radiation
D. All of these

Answer 1

Hint: In order to solve this question we need to understand heat transfer. So heat is defined as a form of energy which transfers from one place to another due to the difference in temperature of two places. It is also regarded as thermal heat. To answer this question, you can proceed by defining each of the given options and later define the condition inside the room and according to that condition which method of heat transfer is most suitable.

Complete answer:
So first let us define each of the given options.
Conduction:It is the mode of heat transfer in solids. When we heat one end of a solid rod atom at that place starts vibrating about its mean position, since the interatomic distance in solid is very less so due to vibration of atoms neighboring atoms starts vibrating after collision, in this heat transfer takes place in solid. In conduction heat transfer is done using phonons exchange.

Convection:It is a mode of heat transfer in liquid and gases. In this mode of heat transfer, gases when they become hot then rise upward in the sky and cold gases take the position of hot gases. In this way heat is transferred. In convection heat transfer is done by exchange of matter with surroundings.

Radiation:It is a mode of heat transfer in which no matter is exchanged and also it does not transfer due to atoms vibration rather in radiation light waves carry energy in form of photons. For example heat transfer by a blackbody to the surrounding is done by radiation.In a closed gases trap so when heated around a place, gases at that place become hot and rise upward and cold air takes the position of hot gases. In this way heat transfer is done in a closed room and this condition is fulfilled by Convection mode of heat transfer.

Therefore,the correct answer is B.

Note: It should be remembered that phonons and photons only came into existence after quantum theory got developed, before that heat transfer was only considered as energy transfer carried by heat waves in nature. Due to convection, clouds with water form in the sky which later after condensation falls back on earth.