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Unformatted text preview: MIT Society of Physics Students Outreach Prepared by Anjali Tripathi & Colin Hill Line Spectra Demonstration Learning goals:- Introduce the electromagnetic spectrum - Learn the meaning of diffraction - Learn that certain elements have certain spectral signatures, which allows us to identify different materials (stars, planets, etc) More advanced topics to cover: - Spectra result from atoms getting excited by collisions and electricity in the gas discharge tube so they emit light. - Everything emits radiation, including students themselves (but it's in the Infrared which is why we can't see it without a thermal camera) - Neon, fluorescent, etc. lighting emit discrete spectra, while incandescent bulbs emit continuous spectra Materials:-Gas discharge tubes & power supply -Diffraction gratings -Handouts -Pens/pencils Procedure: We will begin as a group for about 5 minutes and have a 'lecture' format with the students. We'll introduce ourselves – name, class year and research interests – and why we're looking at line spectra today (ability to determine composition elsewhere, etc) Then we'll break off into 3 groups i.e. 2 undergrads in each group. As a subgroup: Begin by asking students if they've ever seen rainbows from a CD. If they say no, don't worry. Tell them they'll get to see the effect you were describing, but even better. Hand out diffraction gratings and a handout to each student. Explain to them that a diffraction grating is something that has lots of little grooves on the surface. Their gratings have 1000 lines/mm, i.e. 19000 lines on their tiny grating! The small spacing between grooves allows incoming light to be cut, as it goes through the grating. This 'cutting' of the light is known as diffraction . The cool thing about the diffraction grating is that you can see how the incoming light has been cut up into different parts, which are different colors. Different colors come from something known as wavelength, which is a property of waves of light and all light can be thought of as waves. The wavelength representing each color in the visible spectrum is found on their grating. wavelength representing each color in the visible spectrum is found on their grating....
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This note was uploaded on 11/27/2011 for the course AST 301 taught by Professor Harvey during the Spring '07 term at University of Texas at Austin.
- Spring '07