Three mirrors side by side

The idea

A plane mirror always forms an erect image of the same size as the object, while in spherical mirrors image size changes with object distance; all three types show lateral inversion.

Walking away from a mirror

You stand in front of a plane mirror, the flat kind on a wall. Then you slowly walk away from it.

What happens to the size of your image?

• It stays the same size as you
• It becomes smaller
• It becomes bigger

One card, three mirrors

A card with the letter F faces a plane, a concave and a convex mirror. Put it near, then farther, then far. Look at the size, at which way up it is, and at the letter's left and right.

Plane stays the same

A plane mirror always forms an erect image of the same size as the object. In spherical mirrors, the image size changes as the object's distance changes. All three types show lateral inversion.

Lateral inversion: in the image, left and right are swapped, as you saw with the F. A neat idea from the book: you can tell whether a mirror is plane, concave or convex just by looking at the images in it!

• Mirror | Image as the object moves away
• Plane | Always erect, always the same size
• Concave | Erect and enlarged when near; inverted farther away; size changes
• Convex | Always erect and diminished; size changes

Notes

A plane mirror always forms an erect image of the same size. In spherical mirrors, image size changes with the object's distance. All three show lateral inversion.

Check yourself

You walk away from a plane mirror. What happens to the size of your image?

In which mirrors does the size of the image change as the object moves away?

Which mirrors show lateral inversion, with left and right swapped?

Three mirrors look alike. In one, your face looks large and erect when you are close, and upside down when you step back. Which mirror is it?

• It becomes bigger. A plane mirror's image is always the same size as the object.
• It becomes smaller. It may look smaller to your eyes, like anything far away. But the image itself is always the same size as you.
• It stays the same size as you — correct. Yes. A plane mirror always forms an image of the same size as the object.
• Only plane mirrors. A plane mirror's image is always the same size.
• Concave and convex mirrors — correct. Yes. In spherical mirrors, the image size changes with the object's distance.
• In no mirror. In concave and convex mirrors, the image size does change.
• All three: plane, concave and convex — correct. Yes. Lateral inversion is seen in all three types.
• Only plane mirrors. Concave and convex mirrors swap left and right too.
• Only spherical mirrors. A plane mirror also swaps left and right. Think of reading writing in a mirror.
• A plane mirror. A plane mirror's image is always erect and the same size.
• A convex mirror. A convex mirror's image is always erect and smaller.
• A concave mirror — correct. Yes. Near: erect and enlarged. Farther: inverted.