Reflection and Making a Cellphone “Hologram”

 Reflection

The property of reflection may well be the property of light we are most familiar with and dependent upon. After all, without reflection we wouldn’t be able to see. Light, either from a natural or an artificial source, leaves the source and bounces off an object (reflects). If the light reaches our eyes, we can see the object.

Once we understand the various properties of light, such as reflection, we can develop technologies that use the properties. For example, we use reflection for mirrors, telescopes, and microscopes. Some makeup manufacturers even use an understanding of reflection to produce makeup that makes our skin look smoother and more perfect than it really is.

We can also have fun with understanding light—how about “holo” nail polish? There will have to be a separate posting on that, because the science is more involved than simple reflection. But the cellphone “hologram” does, in fact, use simple reflection.

Thanks to Randy Attwood for help making the video.

Making a Cellphone “Hologram”

There are many sites on the Internet that describe how to do this. Just search for “make a phone hologram.” Here’s what I did to make the cellphone “hologram” in the video.

Materials

You need a piece of clear plastic; it must be relatively rigid but doesn’t need to be 100% rigid. Some sites recommend a clear CD case, but that can be tough to cut using an Exacto knife, especially if you want to involve kids. I used the clear plastic covering, or lid, from a box of Christmas cards. You could also use a transparency, if you have one lying around. You’re going to cut out 4 pieces to make a trapezoid, which needs to be able to support itself when the pieces are taped together. So keep that in mind while choosing your clear plastic material. And it must be large enough that you can cut all 4 trapezoids from it. For an idea of size, see the image below; it has dimensions on it.

  • Pencil
  • Ruler
  • Graph paper is helpful but not necessary.
  • Scissors or Exacto knife (have kids use scissors; adults can use the Exacto knife)
  • Clear tape
  • Cellphone with Internet

Instructions

  • Draw four trapezoids on the clear plastic. See dimensions below. Don’t change the dimensions. We want to end up with a specific angle of reflection.

  • Cut them out.
  • Tape them together, with a slanted side attached to another slanted side. You want to end up with a free-standing object, so all sides are joined.

  • On the cellphone, search YouTube with the term “phone holograms”; for example, the video I used is from here: https://www.youtube.com/watch?v=BZ6fun_RKfk 
  • Make sure the brigthness setting on the cellphone is at its highest.
  • Have the cellphone on a table or desk such that people can crouch down and be eye level with the flat phone. Have the video on the cellphone ready to play. Place the structure, small opening on the bottom, on the phone over the video. Crouch down to be eye level with the phone. Start the video, and turn out the lights and watch the “holograms.” They are faint and best seen in a darkened room.

I keep using quotes when I refer to the cellphone “hologram” because these are not real holograms. They are light reflections. They just look like holograms, which makes them so cool. You need lasers, mirrors, and wave interference to make a real hologram.

The Science

The dimensions of the trapezoids are such that the sides are designed to be at a 45º angle to the surface of the phone. When you reflect an image in a transparent screen (the clear plastic) at that angle, you see a “virtual” image, which is just a reflection of what the cellphone screen is playing.

You can have your kids or students view the images from each side of the plastic trapezoid. They may be able to figure out that they see the image of the video on the side they are watching.

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