It will be useful to have a way to make a mirror stand up by itself. Taping it to a block of wood works well, or you can fold an index card into three panels and tape the middle panel to the back of the mirror. The mirror needs to be pretty nearly vertical, and not visibily leaning forwards or backwards. The following activities will work slightly better if the mirror is standing up the tall way, so that it looks more like a door than a billboard.

Now set up a light station that produces a sharp light beam crossing a flat white screen on the table top.  Do the following three activities:

1. Put the mirror in the beam, and adjust its position so that the beam both entering and leaving the mirror is displayed on the white paper  Observe how the reflected beam depends on the position and orientation of the mirror.  Compare this to what happens when you put a white card in the beam (standing up the same way as was the mirror), and what happens when you put in a piece of aluminum foil that has been slightly crinkled (making a sort of mirror with a surface that is not quite smooth).

In each case light is reflected -- that is, it gets redirected by the object in the beam. We will call the reflection by the card diffuse reflection, and reflection by the mirror mirror reflection; the crinkled aluminum foil is somewhere in between, depending on how enthusiastically you crumpled it.
2. For several placements of the mirror in the beam, measure the angle between the incoming beam and the surface of the mirror, and the angle between the reflected beam and the surface of the mirror.  (These are angles A and B shown on figure below.)  How are these related? 
   
3. Here's a way to make sure that you really understand mirror reflection. Set up the light station so that it is making a nice beam across a piece of blank paper. Now suppose you want to make the beam hit a particular target, which requires sending it around several corners. We can do this with mirrors, of course, and the easy way to hit the target is to move the mirrors around with the light beam turned on until everything works. But we are going to do it the hard way, placing the mirrors with the light beam turned off!

   Before you turn off the light beam, use a ruler to draw a line down the center of the beam on the viewing screen (the sheet of white paper on the tabletop). Then turn off the light, being very careful not to disturb the position of anything (it might be a good idea to tape down everything before drawing the line). 

   Place the first mirror somewhere intersecting the beam at some angle to it that you think will deflect the beam in an interesting way, and draw a line along the front edge of the mirror. By measuring angles, predict where the beam will go next after it is reflected by this mirror, and draw a line on the paper to represent this. Then place another mirror intersecting this line, and again mark its position and draw a line that predicts where the beam will go. Draw an X somewhere along this line, representing the target the beam is going to hit.

   Now turn on the light, and see where the beam actually goes!
   Here is a photograph showing a possible path for the beam and a target. The mirrors are not in their right places yet.
   
   

   Actually hitting the target is hard -- it requires measuring all of the angles to within a few degrees. But you should be close enough that you are able to hit the target by moving the mirrors only a little bit; if not, you should measure the angles again, to see what went wrong.

   This is an important and useful exercise. Write some notes to yourself about any problems you had setting up the activity, and what went wrong while doing it, to make it easier when you try this in your classroom.

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Science content: mirrors