The temperature in a spherical reflector type solar cooker is raised to more than $500\;^\circ C$ by :

A Concentrating energy at one point by using a concave reflector
B Proper insulation of the cooker
C Concentrating energy at one point by using a convex reflector
D Both (A) and (B)

Hint:A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurize drink and other food materials. As solar cookers do not make use of any fuel and cost nothing to operate, solar cookers help reduce fuel costs and air pollution.

Complete step by step answer:
The working principle of a solar cooker comprises three steps: concentrating sunlight, converting light energy to heat energy, and trapping heat energy. The reflector installed on top of the solar cooker is a mirrored surface with high specular reflection, which is used to concentrate light from the sun into the small cooking area. Specular reflection means that the incident light is reflected into a single outgoing direction. The mirror used in the reflector is a convex mirror of focal length equal to the distance between the mirror and the inside of the cooker. We know that light rays coming from the sun and the sun can be considered to be at an infinite distance from us. Light rays coming from infinity and being incident on a convex mirror are converged at the focal length of the mirror. These concentrated and focused light rays help raise the temperature of the cooker for cooking purposes.
The temperature in a spherical reflector type solar cooler is raided to more than $500^\circ$C by concentrating energy at one point by using a concave reflector.

Therefore, the correct option is (A).

Note: Solar cookers require constant stirring of food while being cooked. To prevent eye damage from the highly concentrated sun’s rays, users should avoid glaring directly into the insides of a solar cooker. Also, avoid touching the insides of the solar cooker to prevent burns. Also note that after the light is focused, it is converted into heat energy and a solar cooker does not focus on solar energy.