Question

Heat energy received by the earth from sun is due to
A. Convention
B. Radiation
C. Reflection of light
D. Transmission of light

Answer 1

Hint: There is no medium in space. So the heat energy from the sun reaches the Earth’s surface through a process which doesn’t require a medium.

Complete answer:
Only a tiny fraction of total energy of the sun reaches the Earth and it is enough to heat the Earth. Heat can be transferred in three ways- conduction, convection and radiation. The heat transfer between Sun and Earth can’t occur directly because the two bodies are not in contact with each other.
 Conduction is the most common method of heat transfer and it occurs only when two bodies are in contact with each other. Conduction occurs when rapidly moving particles interact with particles of a neighboring object and transfer some of their energy to the latter. Heat can’t be transferred from sun to earth by conduction, because air is a bad conductor of heat.
Convection is the transfer of heat in gases & liquids. Convection occurs when a heated fluid moves away from the source of heat and comes in contact with other substances, transferring some of their energy. So, it is clear that the heat from the Sun can’t be transferred to the earth by the process of conduction and convection.
But, radiation doesn’t require a medium to transfer energy. So, the heat of the Sun is transferred to the Earth without any material medium, by radiation. Heat can be transferred from all resources of light by convection and radiation, but heat is transferred from the Sun by radiation only.
Hence, the correct answer is option (B)

Note: Only Some of the heat energy from the sun reaches the earth’s surface, some of it bounces back off the earth's atmosphere. The energy that reaches the surface warms the earth. The extra energy is used by various chemical reactions, which releases heat again as a by-product. This heat is released through thermal radiation. The heat energy that is trapped by the greenhouse gases in the atmosphere, raises the temperature on earth.