---
title: "A point light source is placed at the focal point \\(F\\) of a concave mirror in an attempt to create a collimated beam of light where all reflected rays travel parallel to the principal axis. An optics student compares two mirror geometries: a parabolic mirror and a spherical mirror of large aperture. Which mirror shape reliably produces a perfectly parallel beam for all rays originating from \\(F\\), and why?"
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url: "https://nerd-notes.com/ubq/117367/"
date_modified: "2026-08-04T06:51:59+00:00"
---

# A point light source is placed at the focal point \(F\) of a concave mirror in an attempt to create a collimated beam of light where all reflected rays travel parallel to the principal axis. An optics student compares two mirror geometries: a parabolic mirror and a spherical mirror of large aperture. Which mirror shape reliably produces a perfectly parallel beam for all rays originating from \(F\), and why?

A point light source is placed at the focal point \(F\) of a concave mirror in an attempt to create a collimated beam of light where all reflected rays travel parallel to the principal axis. An optics student compares two mirror geometries: a parabolic mirror and a spherical mirror of large aperture. Which mirror shape reliably produces a perfectly parallel beam for all rays originating from \(F\), and why?

![A horizontal dashed line representing the principal axis passes through the center of a concave mirror oriented vertically and curving toward the left. On the axis, a small dot labeled S marks the focal point F of the mirror. Exactly four straight solid lines with arrowheads originate from point S and diverge outward, terminating at different locations along the concave reflecting surface. At each termination point on the mirror, a reflected ray extends horizontally toward the left. No other labels, lines, text, or axes appear.](https://nerd-notes.com/wp-content/uploads/ubq-frq-generated/stem-fig-1-1785826318-lFDOyl.jpg)

- **A.** The spherical mirror, because the uniform radius of curvature guarantees that every ray striking any part of the surface reflects parallel to the principal axis.
- **B.** The spherical mirror, because rays striking near the outer edges reflect closer to the principal axis than rays near the center, focusing the beam outward.
- **C.** The parabolic mirror, because rays striking near the outer edge undergo total internal reflection, ensuring all light stays directed forward.
- **D.** The parabolic mirror, because all rays from the focal point reflect parallel to the principal axis, whereas the spherical mirror exhibits spherical aberration for non-paraxial rays.

*The answer key and step-by-step explanation are available to logged-in users at https://nerd-notes.com/ubq/117367/*