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Another name for a laser is a photon gun. A photon is a small particle of light, and a photon gun like the ones we use in the classroom usually shoots out a very large number of photons each second. The number of photons that are emitted at a time is related to the intensity: more photons mean more intensity, which means the laser looks brighter. Photons, No Barrier A. Suppose that the intensity of light that the laser puts out is lowered so that it only emits one photon at a time. Suppose the laser shines at a photographic film directly (without a barrier in the way). A film turns color when a photon hits it, and then stays that color. 1. The big circle represents a normal laser dot (the area in which photons can hit the screen). Sketch what you would see on the plate after ten photons hit in the circle at the right. How is this like what happens with paint balls?



Electrons An electron is like a very, very small paint ball. Without the paint. Like paint balls from paint ball guns, we can shoot electrons from electron guns. Your television has an electron gun in the back. It shoots electrons at the screen, which glows when an electron hits it. Suppose that an electron gun shoots out one electron at a time, and those electrons hit a photographic plate. A photographic plate is like film, and it lets us see where electrons hit. 1. The circle on the right represents the plate. Sketch what you would see on the plate after ten electrons hit it. How is this like what happens with paint balls? © 2003-5, University of Maine Physics Education Research Laboratory. DO NOT DISTRIBUTE 3 2. On the second circle, mark what you would see after a very long time. Explain your reasoning. Is this consistent with the idea of lots of paint balls hitting a wall?