Introduction: Flashlight Investigation

By Lesley STEAM Learning Lab
About: The Lesley STEAM Learning Lab is a center designed to research new opportunities for learning through engagement and inquiry-based exploration. In addition to his work with Lesley, Dr. Goldowsky is principal…

Why explore light? Light is a fundamental and familiar part of the world and yet exploring how light acts can lead to many surprises. Exploring how light interacts with different objects starts to build an understanding of the physics of light. Looking at how light travels and reflects, and how shadows work, brings up mathematical and geometrical concepts including symmetry in approachable ways.

Flashlight Investigation is part of the Light and Shadow Workshop, developed 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 Light and Shadow activities also work well for remote learning, since most materials are readily available or can be supplied in a teaching kit.

The activities are divided into five sessions, although the investigations can be extended well beyond this format. The first session, Flashlight Investigation is outlined here, the other sessions are outlined in separate Instructables.

Light and Shadow

  • Session One: Flashlight Investigation
  • Session Two: Make a Camera Obscura From a Cereal Box — or Practically Anything Else
  • Session Three: Light and Mirror Puzzles
  • Session Four: Paper Cutting, Mirrors, and Symmetry
  • Session Five: Shadow Stage

Supplies

  • Flashlight (any small flashlight with a fairly defined beam should work)
  • A sheet of white printer paper
  • Pencil or pen
  • Household materials as available


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.

Step 1: Lights and Objects

What can you find out by shining a flashlight through objects and materials around the house? What can we find out about how light travels when it leaves the flashlight?

Find a variety of household materials and see what happens when you shine a flashlight through them. Try putting the flashlight on a sheet of white paper and putting the object into the beam; or shine your flashlight through the object onto the paper.

Give participants time to find and explore different materials. Have participants share the most interesting 3 or 4 objects, and their observations with the group.

If participants are stuck for ideas you might suggest bottles of liquid (shampoo, mouth wash, honey, etc.); paper of various sorts; marbles or plastic toys; plastic or other materials from recycling; clothing; leaves.

You could also have people try to find examples of materials that fall into each of the categories below:

  • Clear (you can see an image through it)
  • Translucent (some light gets through, but you can’t see through it clearly)
  • Opaque (no light gets through)
  • Reflective (light bounces off)

Step 2: Share and Discuss Your Observations

The discussion will depend on what students found and observed. Students may raise any number of different, and interesting, questions -- focus on how they might further investigate their questions.

Below are some phenomena students may notice. The background information is not intended to explain all of the physics involved, but rather to suggest some options for guiding the conversation and pointing towards further investigation. Likewise, the technical terms may be helpful to label a phenomenon and talk about it more easily, but the focus is on exploring the phenomena, not defining the terms. (The Glossary has definitions for the terms in italics.)

Some phenomena that participants may observe:

Clear materials (you can see an image through it)

  • Does it make an interesting pattern if you shine the light through the material onto the sheet of paper? Many clear materials refract light; this can project interesting patterns.
  • Do different sections of your object/material act the same way in the light?
  • Do you see any rainbow colors in the refracted light?

Translucent materials (some light gets through, but you can’t see through it clearly)

  • What happens to the flashlight beam as it passes through the material?
  • How does the beam look along the paper before and after passing through the material?
  • The light from the flashlight is white, but the light coming out the other side of the material may be a color. These materials act as a color filter. White light is a mix of colors, what happened to the other colors?

Opaque materials (no light gets through)

  • What happens to all the light?
  • Does light bounce off the material?
  • Different materials reflect and absorb different proportions of the light that hits them.

What else do you notice?

  • Sometimes shining the flashlight through an object/material can reveal things about the structure of the object. For example, you may see the threads and holes in fabric, or texture in a sheet of paper.
  • Eggs are very interesting to look at, especially if you have a dark room or box. You can put the flashlight right up against the egg. Farmers call this “candling”.
  • Water can be a good lens - try shining the flashlight through a clear jar (or glass) of water. (A closed jar may be better if students are working near their computers!)

Step 3: Glossary

For details beyond these quick definitions, see links in Resources.

Refract - Some materials redirect light rays as they pass through it: they refract the light. Thicker areas of the material will refract the light more. Shining the flashlight through a material like clear plastic onto paper creates interesting patterns of bright lines and darker areas: light is refracted away from some areas, and concentrated in others, while still others are in shadow. Refraction can also separate the colors of light: white light is a mixture of different colors of light, and some colors are refracted more than others. Because of this, refraction can separate the colors, producing a rainbow.

Lens - Lenses are carefully shaped to refract light in useful ways. A magnifying glass is an example of a lens.

Reflect - Light bounces off a reflective surface (the physics is complex, but "bounces" explains the way we see light move). If a reflective surface is very smooth, you can see an image -- the light bounces in an even and organized way. An uneven reflective surface will bounce light in all different directions, scattering it. For example, you can bounce light from your flashlight off a white sheet of paper to light up a dark corner. Every object reflects some of the light that hits it. Light colors reflect more light to our eyes and so look bright, dark colors reflect less light.

Absorb - Light that is not reflected is absorbed. Dark colors absorb the most light and reflect the least. The absorbed energy heats the object -- dark-colored objects in the sun get hotter than light-colored objects because they absorb more light energy. (The sun is much stronger than a flashlight; you can not feel the warming caused by light absorbed from a flashlight).

Color - Light has three primary colors (red, green, blue); together they make up white light. Different intensities of the three primary light colors can be combined into endless different mixed colors. A prism, water drop, or refractive material can separate white light, and we see the colors of the rainbow.

Pigment colors - Paint and other pigments absorb more of some colors of light and reflect more of other colors. We see the (mixed) color of the reflected light since this is what reaches our eyes. For example, when you bounce the light from a flashlight off red paper, you see the reflected red light (or more precisely, a mix with mostly red light, since different shades of red also have a little blue or green mixed in).

Color Filter - If light passes through a clear or translucent material, some colors of light may be absorbed on the way through, and we see the (mixed) colors of light that pass through.

Light Rays - When we talk about light rays, we refer to the fact that light travels in a straight line -- although this path can be redirected when we reflect or refract the light. In terms of physics, light can be described as a traveling photon, or as an electromagnetic wave, and different colors of light can be described as different wavelengths of light.

Step 4: Resources

In-depth introduction to light for teachers:

Shedding Light on Science:https://www.cfa.harvard.edu/smgdvl/sls/index.html

Light to heat: https://www.scientificamerican.com/article/how-ex...


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.