The projection room at the back of a movie theatre is a cool place. That’s because the room has an incredible network of cold air pipes. This frigid air, however, isn’t meant to keep the projectionist comfortable. It is sent straight to the movie-making machines. There, it cools the projectors and the movie film. Without this continual blast of frigid air, the projector and film would be ruined by the intense heat given off by the white-hot projection lamp.
Things Required:
Torch
Discarded 35mm photographic slide
Wax paper
Rubber band
Hand lens
Tape
Directions:
Cover the lens of a torch with a double thickness of wax paper. Be careful not to crumple or wrinkle this paper. (The wax paper lens will “soften” the bright centre of the beam)
Pull the wax paper tight and secure this covering with a rubber band. Place a 35mm slide on top of the wax paper. Use tape to hold the 35mm slide in place.
Turn on the torch. Aim the beam at a light-coloured wall that is at an arm’s length. What do you see? Can you see colours? Is the image clear or fuzzy?
Place a hand lens several inches in front of the slide. Move the lens back and forth. Does the lens sharpen the projected image? Is the projected image larger or smaller than the actual drawn figure?
This Is What Happens:
You’ve built a film projector. Light that was emitted by the bulb streamed through the photographic slide. From there, the light continued outward, spreading as it travelled. By the time these rays struck the wall, the beam produced an out-of-focus image. To prevent the rays from spreading apart, a hand lens was placed into the torch beam. Its shape redirected the rays and focused them on the nearby wall, creating a sharp (and enlarged) image of the 35mm slide.
