Tape the punched card at the 0 centimeter mark on the meter stick so that it stands up perpendicular to the stick. Tape the other card so that it stands up parallel to the first card like a screen at the 100 centimeter mark. Take your meter stick to a sunny area and point the punched card toward the sun. Students work in teams of 3 or 4. Set up the light source near the middle of the room and dim the room lights as much as possible.
Bare bulbs get hot.
Hold up the card with the hole so that light from the source comes through it. It will work best if you are about 1 or 2 meters from the light. Hold your grid card so the square of light falls on it. Measure and record the distance between cards. Again measure and record the distance.