Where is the image in the mirror?

It's not always where you've heard it is.

Introduction

A large lens can be used to make an image in a mirror. The lens allows the image to be placed on the surface of the mirror.

Material

A flat mirror

A very large lens, such as "page magnifier" Fresnel lens, which is a lens as large as a sheet of typing paper.

A minimag light.

To Do and Notice.

Find the focal length of the "page magnifier." Do this by making an image of a distant light source and measuring the distance from the magnifier to the image. The light source should be 20 feet or more away.

Mount the page magnifier two focal lengths from the mirror.

Put the bare lightbulb from a minimag light two focal lengths from the page magnifier.

This will produce an image of the lightbulb visible in the mirror.
Look at this image, notice where it is.

Notice that the image of the lightbulb is on the surface of the mirror.

What's Going On?

An object, like the lightbulb, placed two focal lengths from a page magnifier lens will produce an image two focal lengths from the lens on the other side. Place a mirror at this position and you will produce an image of the light source on the surface of the mirror.

So What?

Many students have memorized the words that tell them that the image of an object in front of a flat mirror is behind the surface of the mirror a distance equal to the distance to the object in front of the mirror. This exploration is designed to use a lens to create an image on the surface of the mirror.