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How does a mirror work?

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Quick answer

A mirror reflects light by the law of reflection: the angle at which light hits the surface equals the angle at which it bounces off. A smooth, polished coating—usually silver or aluminum—ensures that parallel rays stay parallel, so your eyes see a clear, faithful image of whatever is in front of the mirror.

A mirror works by reflecting light according to the law of reflection: the angle of incidence equals the angle of reflection. A smooth, polished surface, usually a thin layer of silver or aluminum behind glass, makes the reflected rays form a clear image of whatever is in front of it.

Step by step

  1. Light from an object travels in straight lines toward the mirror.
  2. The light strikes the mirror's smooth reflective coating, typically silver or aluminum.
  3. Each ray obeys the law of reflection: angle of incidence equals angle of reflection.
  4. The reflected rays travel back to your eyes, preserving their relative directions.
  5. Your brain interprets the pattern of incoming rays as an image located behind the mirror.

Key things to understand

  1. Light travels in straight lines until it hits a surface, where it can be absorbed, transmitted, or reflected.
  2. When light strikes a smooth surface, the angle at which it arrives (angle of incidence) equals the angle at which it bounces off (angle of reflection).
  3. A mirror's reflective coating, typically silver or aluminum, is applied to one side of a flat glass sheet.
  4. The glass protects the reflective coating and also contributes a faint secondary reflection from its front surface.
  5. Because the surface is flat and smooth, parallel light rays bounce off in parallel, preserving the image's shape and allowing you to see a clear reflection.

Labelled diagram

  1. Light source

    An object emits or reflects light that travels toward the mirror.

  2. Incident ray

    A straight line of light approaches the mirror surface.

  3. Reflective coating

    A thin layer of silver or aluminum bounces the light back.

  4. Reflected ray

    The light leaves the mirror at the same angle it arrived.

  5. Observer's eye

    The eye receives the reflected rays and sees a virtual image.

How a mirror reflects light

Real-world examples

  • A bathroom mirror uses a silver coating behind glass to give a clear reflection for daily grooming.
  • A car's side mirror is often convex, curving outward to widen the driver's field of view.
  • A telescope uses a large concave mirror to collect and focus faint light from distant stars.
  • A security mirror in a shop is convex, allowing a wide view of the aisle to prevent theft.

Common mistake

✗ Myth: Mirrors reverse left and right.

✓ Fact: Mirrors actually reverse front and back. When you face a mirror, your right hand appears on the same side as the reflection's left hand because the reflection is facing you, not because left and right are swapped.

People also ask

Why do mirrors reflect light?
Mirrors reflect light because their surface is smooth and coated with a highly reflective metal like silver or aluminum. When light hits this surface, it bounces off according to the law of reflection: the angle of incidence equals the angle of reflection. This preserves the image's details.
What is a mirror made of?
Most mirrors are made of a flat sheet of glass with a thin reflective coating on one side. The coating is typically silver or aluminum, applied by chemical deposition or vacuum coating. The glass protects the metal and provides a smooth surface for clear reflection.
How does a mirror show your reflection?
Light from your body travels to the mirror and reflects back to your eyes. Because the mirror is flat and smooth, the reflected rays preserve their relative directions, so your brain interprets them as an image of yourself located behind the mirror. This is called a virtual image.
Why does a mirror reverse left and right but not up and down?
A mirror does not actually reverse left and right; it reverses front and back. When you face a mirror, your right hand is on the same side as the reflection's left hand because the reflection is facing you, not because left and right are swapped.
What makes a mirror different from a piece of glass?
Ordinary glass transmits most light, so you see through it. A mirror has a reflective coating—usually silver or aluminum—behind the glass that bounces light back, so you see a reflection instead of what is behind the glass.
Why do some mirrors make you look taller or shorter?
Curved mirrors change the way light rays converge or diverge. A concave mirror can magnify, while a convex mirror widens the field of view and makes objects appear smaller. Flat mirrors preserve size and shape.
How is a mirror made?
A thin layer of silver or aluminum is deposited onto one side of a flat glass sheet, often by a chemical or vacuum process. The glass protects the metal and provides a smooth surface for clear reflection.

Part of the guide: Everyday Science: Light, Heat & Matter →