Question

why parabolic mirror is used in headlights

Answer 1

Dear student,

parabolic mirrors work better to produce nice, tight beams of light. It will be easier to explain if we turn the process backwards for just a moment, and consider what happens when a nice beam of light strikes a mirror. If the mirror is flat, then the beam just bounces off and continues in a straight line. The beam retains the same width and shape it had before it struck the mirror. But if beam of parallel light rays strikes a parabolic mirror, something very special happens. The light rays near the outer edges of the beam hit the mirror at some gentle angle, which directs them in a new direction. The light rays near the center of the beam strike the mirror more directly, and are thus reflected in a slightly different direction. However, it turns out that the slightly different directions given to the light rays in different portions of the beam cause them to all converge to a single spot: the focus of the mirror.