Question

What is the primary source of energy ?
a.) Tides
b.) Wood
c.) Cow dunk
d.) Sun

Answer 1

Hint: The primary source is the one that can be used for most of our functions. If this source is only left, then even all our energy requirements can be fulfilled. It should be a high source of energy. From the above options, the correct answer is the star.

Complete answer:
The word primary means basic. The source which is ultimately required and can not be replaced. We all know that we need energy for all our daily work from cooking to running vehicles. Every machine needs fuel which provides it energy to run. Even our body requires energy to perform all the functions. We obtain our energy from food.
So, the primary source of energy is the Sun because the rays of Earth, when coming to earth, are trapped by molecules which are used later on. The complete energy on our planet is given by the sun in the form of radiations. These radiations when reaching earth strike at the surface of molecules. These molecules absorb some of their energy. Thus, their energy gets decreased and as a result, the radiations can not go back in outer space. So, these remain in the atmosphere and thus, heat it which is the basic necessity.
If we see the options, we see the first is tides. The tides give us tidal energy which is produced by natural rise and fall of ocean tides and current. A large amount of electricity is generated in this way but we can not completely depend on tides. It is a natural phenomenon. There are areas where seas are not present, so; how would those areas get energy. Further, only a limited amount of energy is produced that can not fill all needs.
The second option is wood. The trees and cutting at a large scale. Only wood can not provide energy for all needs as much required. So, it can not be the primary source.
The third option is the cow dunk. The cow dung is produced from cows. It is not present in such a large quantity that it could be considered a primary source. Not much energy could be produced from cow dunks. So, the Sun is the only source which has a large amount of energy and can be regarded as the primary source.

Thus, the option d.) is the correct answer.

Note: It must be noted that the Sun is a star and has a large amount of energy due to continuous fission and fusion reactions taking place in it. Its energy would take millions of years to be used while other sources can be used early. Further, energy from the sun can be used to do all the works from cooking to converting into electricity and many more.