Question

Clear nights are colder than cloudy nights because of
A. Conduction
B. Condensation
C. Radiation
D. Insolation

Answer 1

Hint: Radiation from the sun reaches the earth and heats the earth’s surface. At night, when no sunlight is present, the heat which is trapped inside the earth’s surface gets released into the atmosphere in the form of infrared radiation.

Complete step by step answer:

The radiation from the sun which is an important source of energy for earth reaches the earth in the form of radiation. Some of the energy is absorbed by the atmosphere, especially the ultraviolet rays from the sun, which are harmful to human skin cells and eyes. Rest of the energy is absorbed by the earth’s surface.
So this absorption of energy produces a heating effect which is present during the daytime. At night time the absorbed radiation is emitted back into the atmosphere. These radiations are mostly infrared radiation which is not visible to the human eye. So this radiation which is emitted back, most of it is trapped by the earth’s atmosphere in order to produce the greenhouse effect on the earth and the rest of the energy is released into space.

This is the reason why at night we feel less hot than daytime. When there are clouds present in the sky, the clouds prevent infrared radiation from escaping into the atmosphere. So the heat is still present near the surface of the earth, as a result, we feel a higher temperature compared to a cloudless night.

So the answer to the question is option (C)-Radiation

Note: Radiation is the fastest form of heat transfer, heat is transferred as electromagnetic waves in radiation. So, it will have a velocity equal to the speed of light in vacuum. It doesn’t need any material medium to transfer heat.

Other types of heat transfer mechanisms other than radiation are,

1.) Conduction: It is the type of radiation in which heat is transferred in the form of vibrations of atoms in a solid. If a solid is heated at one end, the atoms at that end gain more kinetic energy from the heat and transfer it to the adjoining atoms. So after some time, the heat provided at one end will be distributed uniformly throughout the solid. This is the slowest mode of heat transfer.

2.) Convection: This type of heat transfer usually occurs in fluids. When a fluid is heated from below, the molecules at the bottom will get less dense than the molecules above. So the denser molecules situated above will come down and the less dense molecules at the bottom will rise up. As a result, heat will be distributed evenly throughout the liquid.