Make a pinhole projector
How to create an optical illusion magic trick in a box
This activity is a wonderful way to get kids interested in science and the wonder of the world.
First of all you need to create a small hole in one end of your shoebox. Push a drawing pin into the middle of one end to make a small circular hole.
You now need to cut out a rectangular window at the other end of the box. Cut out a rectangle of greaseproof paper a little larger than the window, and tape this securely in place over the window.
Next get your torch and cut another piece of greaseproof paper big enough to cover the lightbulb at the end of the torch. Draw a triangle in the middle of the circle using the black pen and then colour this dark green. Tape the greaseproof paper securely in place over the glass lens of the torch – see pic.
Your projector is now ready to use. Go into a darkened room and position your torch on a surface, turn it on and stand back about 1m. Look through the larger window and point the smaller hole at the light and see what happens.
The projector has created an optical illusion that has flipped the triangle up the other way. As light rays that pass from the top of the torch hit the bottom of the viewer and light rays that pass from the bottom of the torch have hit the top of the viewer. These rays cross over when they pass through the pinholes so you end up seeing the triangle upside down.