Question

At what position should a point source of light be placed in front of a concave mirror to obtain parallel beam of light?Name a device where this property is used

Answer 1

to obtain parallel beam position of object should be at infinity. this property is used in solar furnance

Answer 2

A light source should be placed at the focus of the concave mirror to obtain a parallel beam of light.

• We know that the focus of a concave mirror is the point at which the parallel rays of light converge after reflection.
• From the principle of reversibility of light, we can say that light rays starting from the focus will become parallel after reflection.
• So if we keep a source at the focus of the mirror, we'll obtain a parallel beam of light.
• This property is used in high beam headlights of vehicles where we need light to see far objects.