Images are interesting. When a lens or a mirror or a hologram creates an image, how do we know where the image is? The eyes and brain together use many different clues to figure out where an image is, these clues can lead different people to see the same image located at different positions.

Exhibit 1, Touch the Spring

We begin the day with inspiration by looking at a real image floating in the air created by a concave mirror. This is one of the first exhibits I ever saw at a hands-on science museum as a child and I still love it. The exhibit at the Exploratorium is excellent and should not be missed.

Touch the Spring snack

In our exhibit a spring is seen, you have no difficulty determining exactly where the spring is located, yet when you try to touch the spring your hand passes right through it.

(An alternate exploration uses a commercially available pair of mirrors:

Parabolas Snack)

Exhibit 2, Anti-Gravity Mirror

The second exhibit uses a large plane mirror and asks the question, "where is the image in a mirror located?"

Many people quote an answer, "the image is the same distance behind the mirror that the object is in front of the mirror." I then invite them to prove that statement.

Here is how I go about finding where the image is located:

Image Finding in a Mirror

Finding Images, straws

These activities give good practice at finding out where images are located. However, practice makes perfect, so here are a few other image creation exhibits. Use the tools you learned above to find images created in these exhibits.

Also look at the Giant Lens snack

Find images in the Infra red too: Hot Spot Snack

For a difficult problem in image finding build the snack Cylindrical mirror and try to locate the image.

Look into infinity Snack


Exploration 1, Light Box

A deeper understanding of images can be found by using the Light Box to create images of a filament of a light bulb. The exhibit breaks light from a linear filament up into a number of rays. These rays show how an image is made by a lens, or a mirror.

Light Box Images

Exploration 2 Lasers

The operation of lenses can also be explored using inexpensive laser pointers.

Fresnel Lens and Laser

Scan a laser, lens

I hope these explorations have given you a whole new way to look at images.

Additional explorations

Ray tracing gives you a step by step introduction to finding images using ray tracing, it concentrates on pointing out the lies used in the ray tracing technique.

Image on a Mirror, using a lens an image can be made on the surface of a lens.

Image Finding in a Cylindrical Lens is a good final exam to see if you really understand how images are made and how ray tracing works.

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Scientific Explorations with Paul Doherty

© 1999

23 May 2000