Rainbow Room

Fun with sources and spectral glasses The Rainbow Room

This can be a feature of any science meeting or outreach event. Find a room that can be darkened and set up as many kinds of sources as you can find. Bring students into the room individually or in groups and have them put on their rainbow glasses. It can be a time for free exploration, group discussions or even a more formal lesson such as Spectral Scavenger Hunt. Rainbow Room Light Source Ideas

• Sources from SOCK • Other suggested sources – (not included in SOCK) – Glowsticks – Black – vapor tubes – Glow-in-the-dark balls – Incandescent bulbs – Mini-Maglight – Florescent lamps (unscrew the top for a – Fluorescent liquids good point source) (highliters solution, – Circuit board sources detergent finger painting) – -ball – Spark generators Rainbow room ideas with • Fingerpainting with liquid detergent (Cheer and All work well)---young students like to paint a picture or initials on white paper and then view under • Highliter solutions---take any highliter marker (yellow, green and orange work great) take it apart and put the spongy part in a jar full of water. After a day or so the entire jar glows brilliantly under a blacklight. Spectral Scavenger Hunt

• Informal version---just supply list of light sources and some info about the sources with checkboxes to indicate which sources were examined • Formal version---can include questions about various sources to be observed and a mystery source that they should be able to identify after studying all the sources in the room – See examples on following slides Spectral Scavenger Hunt-V1 A. Which number is the mercury vapor tube source? What are in its rainbow?______Notice that the colors are separated, and that not all of the colors are present. This is called a discrete spectrum. Usually discrete spectra are produced by low density gasses. Can you find other low density gas sources?______What colors does it have? ______Can you find any other light source with the same colors (doesn’t have to be the same shape)?…it probably has the same kind of gas in it, too.

B. Which source has a full rainbow with all the colors (ROYGBIV)?______A full rainbow is also called a continuous spectrum. Solids, liquids, and dense gasses produce continuous spectra. Regular light bulbs, which have a very hot wire in them, are good examples. Look out a window to see another example. (The produces a very nice continuous spectrum.) What happens to a continuous spectrum as the source gets hotter and hotter? Find the variable temperature light bulb source and investigate this. How does the spectrum from a very hot wire differ from a much cooler wire?______C. Some special materials produce a spectrum that is not separated, but that only has some of the colors. Which source has mostly ROYG part of the spectrum but hardly any BIV?______Which has mostly GBIV and hardly any ROY?______D. only produce one color of light (an extremely discrete spectrum). What color lasers are in this room?______Which laser produces the longest wavelength light?______E. What is the mystery source, do you think? Is it a solid, a liquid or a gas? Can you figure out its name? How do you know? Spectral Scavenger Hunt—V2 Can you find a small light source with a rainbow that is mostly red with only a little yellow and green?

What kind of spectrum does a regular light bulb have? a) a full rainbow with all the colors b) a few colors, separated by dark areas c) not really a rainbow but only red d) a rainbow with mostly just blues and greens

Cut a thin slit (1/4” x 2”) in a piece of thick paper and view a fluorescent light with your glasses on through the slit. You should see some colors in the rainbow are brighter than others. Which ones are brighter? How do they compare to the spectrum of Mercury as shown in your textbook or in the VQM software? What do you think this means about what is contained inside a ? The “What is light?” Exercise For students already familiar with many of light’s properties---

• The exercise on the next four slides requires some input from an instructor with lots of experience teaching about light • The students also need to have some experience with diffraction, polarization, black-body radiation and photoelectric effect Student question: What is light? Often given teacher/textbook answers: ...electromagnetic radiation produced when electrons jump from one energy level to another lower level...... transverse waves of oscillating electric and magnetic fields...... quanta of energy that propagate at 186,000 miles per second...... the electromagnetic spectrum—ROYGBIV, Ultra-violet, , microwaves, X-rays, radio waves, gamma rays, television...... a form of energy that is massless and is emitted anytime charged particles are accelerated...... the bosonic mediator of the electromagnetic interaction analogous to the graviton or the gluon, blah, blah, blah... …sometimes a better question is more illuminating… Better teacher response: What is light like? …What is light not like? Newton said: Supporting evidence:

Light is like particles… Young, Fresnel, Huygens, Maxwell Supporting evidence: said: No, Light is like waves… Planck, Einstein, Lenard said: Supporting evidence:

But light is like particles, too… Bohr said: Supporting evidence:

Light is either like particles or waves, but not both at the same time… 21st century scientist: Supporting evidence: (What would you say?) Consider the list below. Which does each item best support, light as particle, wave, or both? 1. Light can produce interference patterns when incident on small objects... 2. Light exhibits polarization phenomena... 3. Light can travel to the earth from the sun... 4. Light produces sharp-edged shadow patterns when shining on a stencil... 5. Sunglasses can block light’s from car hoods but not from shiny walls... 6. Light travels in straight lines at constant speed according to Newton’s First Law... 7. Light exhibits the photoelectric effect... 8. The intensity vs. frequency spectrum emitted by hot solid objects has a peak, eventually diminishing for higher frequencies... 9. Very low intensity beams of light produce interference fringes one photon at a time... 10. Covering one slit in a diffraction experiment eliminates the interference patterns... 11. Blackbody radiation phenomena... 12. Very bright red light will not dislodge electrons from metals, while very dim blue light will... 13. Light refracts toward normal when entering thicker medium... 14. Wiggling a charged particle makes light... 15. Low density gases emit discrete spectra when stimulated… 16. You can see a ringing alarm clock in an evacuated glass bulb, but you cannot hear it... 17. Doppler effect... 18. Ray-tracing and geometric optics... 19. Angle of incidence equals angle of reflection... 20. Light refracts away from normal when entering optically thinner medium… 21. 22. What do you think about this statement of the nature of light from a 21st century scientist?

Anonymous 21st century scientist:

Since light exhibits some phenomena that are characteristic of classical waves but not allowed for classical particles (like interference effects and polarization) and some phenomena that are characteristic of classical particles but not allowed for classical waves (like traveling through empty space and the photoelectric effect), then light, whatever it is, can only be described by models that are most sophisticated than merely classical waves or particles.