What is a parabolic mirror?

What is a parabolic mirror?

• A. A mirror with a flat reflecting surface
• B. A mirror whose reflecting surface has the shape of a parabola
• C. A mirror whose surface is curved like a sphere
• D. A lens that focuses light

Answer: (B)

The key idea is how the shape of a reflecting surface determines where light rays go after they hit it. A mirror whose reflecting surface is shaped like a parabola has the special property that parallel light rays along the axis reflect and converge to a single focal point. That focusing behavior is what makes the parabola useful for gathering or directing light with precision, such as in telescopes or satellite dishes. This is why the description that fits a parabolic mirror is a surface with the shape of a parabola. A flat mirror reflects light but does not bring it to a focus. A spherical mirror can focus, but it doesn’t achieve a perfect single focal point for all incoming parallel rays (it has spherical aberration unless the rays are very close to the axis). A lens focuses light by refraction, not reflection, so it isn’t describing a mirror at all.

The key idea is how the shape of a reflecting surface determines where light rays go after they hit it. A mirror whose reflecting surface is shaped like a parabola has the special property that parallel light rays along the axis reflect and converge to a single focal point. That focusing behavior is what makes the parabola useful for gathering or directing light with precision, such as in telescopes or satellite dishes.

This is why the description that fits a parabolic mirror is a surface with the shape of a parabola. A flat mirror reflects light but does not bring it to a focus. A spherical mirror can focus, but it doesn’t achieve a perfect single focal point for all incoming parallel rays (it has spherical aberration unless the rays are very close to the axis). A lens focuses light by refraction, not reflection, so it isn’t describing a mirror at all.