#4 - Lecture 4 Light and Color for Nonscientists PHYS 1230...

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Lecture 4 Light and Color for Nonscientists PHYS 1230 Geometrical optics of light rays Shadows, eclipses, pinhole camera
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Demonstrations • Shadows from the overhead projector, small bulbs and candles • Compare with shadows from fluorescent light, overhead projector etc
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Concept question The sharpest shadows are from - A) Large bulbs like an overhead projector B) Small bulbs C) Candles D) Other
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Concept question Shadows tell us - A) What direction the light is shining from B) That something is blocking the light C) That light travels in straight lines
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Geometrical optics - shadows • To cast a shadow, you need a light from a fairly concentrated source, such as the sun • The best shadows come from a point source, for example a small light source or candle • To figure out the shadow location, we use geometrical optics - light travels in straight lines Which bulb will give the best shadow? A B
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X-rays were first observed and documented in 1895 by Wilhelm Conrad Roentgen, a German scientist who found them quite by accident when experimenting with vacuum tubes. A week later, he took an X-ray photograph of his wife's hand which clearly revealed her wedding ring and her bones. The photograph electrified the general public and aroused great scientific interest in the new form of radiation. Roentgen called it "X" to indicate it was an unknown type of radiation. The name stuck! The first X-Rays
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When you get an X-ray taken at a hospital, X-ray sensitive film is put on one side of your body, and X-rays are shot through you. At a dentist, the film is put inside your mouth, on one side of your teeth, and X-rays are shot through your jaw, just like in this picture. It doesn't hurt at all - you can't feel X-rays. Because your bones and teeth are dense and absorb more X-rays then your skin does, silhouettes of your bones or teeth are left on the X-ray film while your skin appears transparent. Metal absorbs even more X-rays. When the Sun shines on us at a certain angle, our shadow is projected onto the ground. Similarly, when X-ray light shines on us, it goes through our skin, but allows shadows of our bones to be projected onto and captured by film. This is an X-ray photo of a one year old girl. Can you see the shadow of what she swallowed? Modern X-rays
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Shadows from Large Sources Two light sources throw two shadows.
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