Question

Name the type of mirror used in a solar furnace so that high temperature can be achieved by this device. Is it a concave mirror or a convex mirror?

Answer 1

Hint: A solar furnace is used to obtain high temperatures at a particular point. The mechanism involves solar power falling on a curved or parabolic surface, reflection from the curved surface and obtaining high temperatures at a particular point. A converging mirror would be the best choice for the construction of curved surfaces.

Complete step by step answer:
A solar furnace is a structure used to concentrate solar power to a particular point and to obtain high temperatures at that particular point. It uses parallel rays of sun to obtain this high temperature. It consists of a curved surface, usually a mirror, to concentrate the solar power from the sun. Solar furnaces are used to generate electricity as well as for other industrial purposes such as construction of nanomaterials and the melting process of steel.
A converging mirror is the best choice to build the parabolic surface, seen in solar furnaces. The mirrors which can converge light are nothing but concave mirrors. Concave mirrors have the capability of concentrating parallel rays of light towards its focal point. So, when large concave mirrors of high radius of curvature are built, they can be utilised for concentrating solar power to its focal point. This causes the generation of high temperature at the focal point of the concave mirror. This temperature can further be utilised for industrial purposes.
The reflection of parallel light rays from a concave mirror is as shown in the following ray diagram.

Clearly, parallel light rays from the sun are concentrated towards the focal point of the concave mirror, after reflection from the concave surface.
Additional information: The largest solar furnace started in the year 1970 and is located in France. With the help of concave mirrors used in this solar furnace, it can obtain temperatures up to $3500{}^\circ C$. Such high temperatures obtained here are used to carry out research in scientific industries like aviation and aerospace industry.

Note:
The same principle as in solar furnaces is stolen to make solar cookers and solar water pasteurisation systems. Light energy from the sun is concentrated to a particular point, where food and water is placed. The high temperature generated at this point is utilised for cooking food in solar cookers and to purify water in pasteurisation systems.