# Reflection & Plane Mirrors - law of reflection, mirror images, pinhole camera

> Interactive school optics: test the law of reflection, specular vs diffuse reflection, plane mirror images, two mirrors, periscope and pinhole camera.

- URL: https://qilingtools.com/en/physics/plane-mirror
- Category: Physics Tools (https://qilingtools.com/en/physics)
- Tags: [Physics](https://qilingtools.com/en/tags/physics), [Education](https://qilingtools.com/en/tags/education)
- Last updated: 2026-10-29
- Price: Free, no sign-up
- Privacy: Runs locally in the browser; files are never uploaded

Covers the light and reflection chapter of middle-school physics. Drag the incident ray across a protractor board to read the angles of incidence and reflection, see that light paths are reversible and that a folded board hides the reflected ray, and compare smooth and rough surfaces. Construct plane mirror images by ray tracing or symmetry to see why the image is virtual, and run the glass plate and two candles experiment on graph paper. It also covers images in two mirrors with a kaleidoscope view, the periscope, the pinhole camera, and umbra and penumbra shadows.

## How to use

1. Pick a tab: law of reflection, specular/diffuse, plane mirror image, glass plate lab, two mirrors, periscope, or pinhole and shadows
2. Drag the light source, object, eye or candles, and adjust mirror angle, hole size or distances with the sliders
3. Read the angle values, image properties and notes to see the rule
4. Try the Practice tab: calculations, mirror clocks and drawing mirror images, all marked instantly

## Features

- Draggable incident ray with angle of incidence, angle of reflection and angle to the mirror. Turning the mirror by α turns the ray by 2α
- Reversible light paths and the folded-board demo showing the rays and normal share one plane
- Plane mirror images by ray tracing or symmetry, animated step by step
- Glass plate lab: candle B snaps onto the image, with recorded data and demos of a thick plate, a tilted plate and a screen that catches nothing
- Two-mirror image count compared with n = 360°/θ − 1, a kaleidoscope view and a periscope ray diagram
- Pinhole camera (image size, hole shape, blur), umbra and penumbra, and practice including drawing questions

## FAQ

### Is the angle of incidence measured from the mirror?

No. It is the angle between the incident ray and the normal, the line perpendicular to the mirror. The angle of reflection is likewise measured from the normal. If you are given the angle β between the ray and the mirror, the angle of incidence is 90° − β. Light hitting the mirror head-on has both angles equal to 0°.

### Does my image get bigger as I walk toward a mirror?

No. A plane mirror image is always the same size as the object, however far away it is. It only looks bigger because it is closer to your eye and fills a larger angle of view, the same reason near things look big. The image itself doesn’t change.

### Why use a glass plate instead of a mirror, and why two identical candles?

Glass both reflects an image and lets you see candle B behind it, so you can find exactly where the image is. A mirror is opaque. Because the candles are identical, B lining up perfectly with A’s image shows the image is the same size as the object. The plate must be vertical, otherwise the image sits too high or low and B can never line up.

### How many images do two mirrors at angle θ form?

When 360°/θ is a whole number you usually get 360°/θ − 1 images: 3 at 90°, 5 at 60°, 7 at 45°. If 360°/θ is odd, that holds only for an object on the bisector. Parallel mirrors give endless images. In the tool you can drag the object and see the real count and how many reflections made each image.

### What does a pinhole camera image look like, and does the hole shape matter?

Light travels in straight lines, so a pinhole gives an inverted real image whose shape is the object’s, not the hole’s, as long as the hole is small. Its size follows h′/H = v/u, so a farther screen gives a bigger image. A large hole turns each point into a spot, blurring the image toward the hole’s shape. Round patches of light under trees are images of the Sun.

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