St. Lawrence University: Physics - Lecture/Demos: Scattered Light

	Scattered Light – Blue Sky & Red Sunsets
Description:	Demonstrates that blue light is scattered more than red.
Notes:	A fish tank with water is set up in front of a slide projector; the projector has a slide with a circular aperture. Students should note the color of the light beam through the tank (it's visible because of scattering due to the the schmutz in Bewkes Hall water), as well as the (white) circle projected on the screen. Gently pour in a little powdered milk (very little is needed), stirring it well. The beam is now easily seen from the side of the fish tank, and takes on a distinctly bluish tinge on the side of the tank closest to the projector, and appears reddish towards the other end. And the circle projected on the screen turns very orange/red. Don't use too much powdered milk, or the projected image will be diminished too much.
Location:	NMSR-DD5: We now own three fish tanks. Grab one that doesn't look like it will leak all over you NMSR: Lab cart. The flat-top cart is particularly well suited for this task. It's a bit taller than the standard carts, and easy to maneuver NMSR: The slide projector lives in the stockroom NMSR-HH3: Use a long glass thermometer for stirring NMSR-J2: Use 3 wood drafting boards to elevate tank; a 2×4 will tilt the projector to proper height for side screen in the astro lab Jeff's Stash: An extension cord, slide carousel, powdered milk and the slide with circular aperture are in his office. Paper Towels: Grab a bunch because you will make a mess!
Image:	Place the tank on 3 drafting boards. Use a 2×4 chunk to elevate front of projector	Impurities in the water will scatter the light
	Before: The white light circle projected through the tank	After: A reddish 'sunset' is projected on the screen
	After: the beam looks bluer closer to the projector, redder farther away

Return To SLU Physics Astronomy Demos


©	St. Lawrence University	Department of Physics