Image Formed by a Plane Mirror

Key points

• Rays from an object reflect off the mirror; traced back, they appear to come from one point behind the mirror: the image.
• The image is as far behind the mirror as the object is in front (2 m in front → 4 m from you).
• It is virtual (cannot be caught on a screen) and erect, and the same size as the object.
• It is laterally inverted: your right hand appears as the image's left (hence the mirror-written AMBULANCE).

Properties of the image

How the image forms

• Two rays leave the top of the object and strike the mirror.
• Each reflects with angle of reflection = angle of incidence.
• The reflected rays diverge; the eye traces them straight back.
• The dashed extensions meet behind the mirror: the virtual image.

Worked example

Object 2 m in front → image 2 m behind → you to image = 2 + 2 = 4 m

If you walk 1 m towards the mirror, the image also moves 1 m towards it, so the distance between you and your image falls by 2 m.

Try it yourself

Goal: Move the object and the eye, and find out what sets where the image is and whether you can see it.

• Drag the object (or use the slider) and compare its distance from the mirror with the image's.
• Press Walk 1 m closer and see how much the gap to your image changes.
• Drag the eye: do the rays change? Does the image move?
• Move the eye far to one side until no ray reaches it.
• Type a word and see what the mirror does to it.

Open the simulation full screen

Quick quiz

3 questions. Choose an answer for each, then submit to see your score and the explanations.