Light and Mirror Puzzles

Mirrors are familiar, but also full of surprises. Investigating how mirrors work can help build an understanding of how light travels in straight lines, and how a mirror can redirect the light to travel in a new direction.

Light and Mirror Puzzles was developed as part of the Light and Shadow Workshop, a workshop using basic tools -- mirrors, lenses, and flashlights -- as the basis for explorations that can help build an intuitive understanding of how light works. Designed for out-of-school-time educators, the workshop is easily adaptable to other educational settings. The activities also work well for remote learning, since most materials are readily available or can be supplied in a teaching kit.

• Flashlight
• Two Mirrors (Plastic mirrors sold for classroom use are safest, but any reasonably stiff mirrored material will work. Be careful of sharp edges.)
• Tape
• Scissors
• Food cans, or small boxes
• Three paper towel and/or toilet paper tubes (you can substitute tubes made from a rolled sheet of paper or cardboard as available)

This activity works best in a semi-dark room. It should be dark enough to see the flashlight beam if you shine it along a sheet of paper. You can also try making a dark area under a table, or setting up the activity inside a cardboard box.

Be Safe: Do not look directly into the flashlight. Household LED flashlights can cause temporary vision spots. Do not use high-power or “tactical” flashlights, or laser pointers, for these activities.

Spend a bit of time experiencing how the flashlight and mirrors work.

Try putting the flashlight on a table so the beam shines across a sheet of paper. If the flashlight does not lie parallel to the table, you can rest the handle on a book, or tape a strip of cardboard around the handle, so that the beam shines along the paper.

• What happens when you put a mirror in the beam?
• What happens when you keep the mirror at 90 degrees to the table, or when you tilt the mirror?

Here are some more ideas to try, or invent your own challenge:

• What happens if you put the mirror flat on the floor facing up, step back, and shine the flashlight at it?
• Can you get the beam to bounce off the mirror and light up different spots on the ceiling?
• If there is an overhead light in the room can you get the flashlight beam to light that up?
• Put the mirror face-up on a table. Pick a spot on the wall (perhaps a picture or calendar). Pointing your flashlight at the mirror, can you light up the spot on the wall?
• Put the flashlight down on the edge of the table so the beam is pointing off the table. Can you hold a mirror in the beam and light up different objects?
• Put your flashlight on the table, shining along a piece of paper. You should see the beam of the flashlight spreading out as it gets further from the flashlight. Using two mirrors can you change the shape of the beam?

What did you notice about how the light and mirror worked?

The mirror maze challenge is a fun way to practice directing light with mirrors under slightly more controlled conditions. Since the mirrors are held vertically, it may be easier to see that light hitting a mirror always bounces off at the same angle relative to the mirror.

To set up, tape your two mirrors to two (unopened) food cans. If your mirrors have an adhesive backing you can use this rather than tape. (In place of a food can, you could use a wooden block, a small box like a box of teabags; anything that will make a stable base for the mirrors and will hold them perpendicular to the table.)

Many flashlights don’t lie flat on a table since they have a wider lens in the front and a thinner handle. If so, tape a strip of cardboard around the handle, so the flashlight lays parallel to the table and the beam is visible along the table.

You will also need three toilet paper tubes. (You can substitute paper towel tubes cut in half, or make tubes with a sheet of paper cut in half the short way. Longer tubes will also work, but are more challenging.)

Finally, you need a small object such as a plastic toy or figurine.

Try the mirror maze challenge:

• Turn on the flashlight and put it on the table, so the beam shines along the table.
• Put your small object somewhere on the table (not in the flashlight beam).
• Now try to arrange all three toilet paper tubes, and both mirrors, to get the flashlight to light up the object. The mirrors and tubes can be in any order or arrangement, but to meet the challenge the light needs to go through all three tubes and bounce off both mirrors, before lighting up the object.
• Can you come up with several different arrangements?

Mirrors are used in many practical ways (in addition to just hanging on the wall), including in cameras, projectors, and periscopes. Mirrors are also used behind the light source in flashlights, ceiling lights, and car lights in order to direct all the light in the most useful direction. (Not all reflective surfaces are smooth and flat enough to reflect an image; for example, a white surface behind a light still reflects light.)

Discuss what people learned from their experiments with mirrors and flashlights. What are your conclusions about how light travels and how mirrors affect the path of the light?

What was surprising? What was beautiful?

Have fun and share photos of your creations!

Periscopes (seeing around corners with mirrors):
https://www.instructables.com/Super-Stealthy-Spy-P...

(And many other versions in Instructables)

Solar ovens (using mirrors to direct light):

https://www.instructables.com/Solar-Oven-2/

(And many others on Instructables)

Exploratorium Mirror Activities:

https://www.exploratorium.edu/snacks/tag/mirror

This work is made possible by support from STAR, a Biogen Foundation Initiative. The team at Lesley supporting this initiative includes faculty and staff in the Lesley STEAM Learning Lab, Science in Education, the Center for Mathematics Achievement, and other related Lesley University departments and programs.