Question

Answer the following questions. Why are concave mirrors used in solar devices?

Answer 1

Hint: Concave mirrors are mirrors which are curved inwards and can form both real and virtual images depending on the position of the object. The radiations coming from the sun are coming from infinity so the case for objects at infinity can be applied for the concave mirror.

Complete answer:
There are three types of mirrors; concave, convex and plane mirrors.
Concave mirrors are those mirrors which are curved inwards. They can form both virtual and real images depending on the position of the object. Its focal length is always negative.
When an object is kept at infinity, the rays coming from the object at infinity, after reflection from the concave mirror pass through the focus. Therefore, we can say that all the rays coming from infinity meet at the focus of the mirror. Therefore, in solar devices, the sun rays after reflection from the mirror get collected at the focus which are converted to electricity or their energy is used as required. Using concave mirrors in solar devices enables us to collect more sun rays.
Therefore, we use concave mirrors in solar devices in order to collect maximum heat radiations coming from the sun.

Note:
By convention all distances taken from left to right of the principal axis are taken as positive and all distances taken from right to left are taken as negative. Concave mirror is known as the converging lens while the convex lens is known as the diverging lens. Image formed at focus is real and inverted.