SPECTROSCOPY
Author(s)
Mark Pichaj.
Description of Equipment
A spectroscope scatters light into its component colors by means of a prism or diffraction grating. The colors we view correspond to the wavelength and frequency of the light.
Students using home-made spectroscopes to study light!
Principles Illustrated
• White light has a spectrum of component colors ranging from red to violet
• Light is electromagnetic radiation, with a wavelength, frequency and velocity.
• Light can be scattered into its component wavelengths through refraction and diffraction.
Photographs & Movies of Demonstrations
> Spectroscopes scatter light ("diffraction" by a grating or "refraction" by a prism) to disclose the hidden nature of light: that it is made of a combination of different wavelengths and frequencies.
Here is a classic spectroscope, as improved by Gustav Kirchoff:
Kirchoff and his improved three-lens spectroscope.
And here is a schematic diagram of how a simple student spectroscope works:
"How a spectroscope works."
And here is another, more detailed view of how a spectroscope analyzes light:
Finding bright line and dark line spectra.
The spectrum of white light is shown by refracting the light through a prism.
"The Spectrum Song"...as sung by Ludwig von Drake (Disney)
Flame tests of different metal salts, showing their characteristic emission spectra.
An even more dramatic, macro, demonstration of elemental emission spectra!
Topics Addressed
> The Sun, and Fraunhoffer lines (dark-line spectra):
GALILEO'S RULE ONE: NEVER LOOK DIRECTLY AT THE SUN !!!
(Instead, keep the Sun at your back, and observe the Sun indirectly, by light
reflected from clouds or a white building.)
> Discovering The Mercury Plasma Above Your Heads: Comparing Spectra Analytically
Hg-vapor lamps?
Fluorescent Lights?
> Simple Atomic Spectra: Gas Discharge Tubes
CAUTION: High Voltage! Hot!
Bright-line spectra: H, He, Ne, Ar, etc.
Harmonic spectral lines: N2 gives a "molecular" spectrum
> Continuous Spectra: Incandescent Light Bulbs
Connect the bulb to a rheostat, vary the brightness of the bulb, and observe the
spectrum! What happens to the high frequency/energy light as the bulb dims?
Standards
Grades Nine-Twelve / Physics / Waves
Waves have characteristic properties that do not depend on the type of wave. As a basis for understanding this concept:
Students know waves carry energy from one place to another.
Students know how to identify transverse and longitudinal waves in mechanical media, such as springs and ropes, and on the earth (seismic waves).
Students know how to solve problems involving wavelength, frequency, and wave speed.
Students know sound is a longitudinal wave whose speed depends on the properties of the medium in which it propagates.
Students know radio waves, light, and X-rays are different wavelength bands in the spectrum of electromagnetic waves whose speed in a vacuum is approximately 3×108 m/s (186,000 miles/second).
Students know how to identify the characteristic properties of waves: interference (beats), diffraction, refraction, Doppler effect, and polarization.
Study Guide Questions
"Use this demo to teach..."
> The fundamentals of spectroscopy. (A good webpage from the U. of Chicago.)
> The nature of light.
> The electronic structure of atoms.
> The chemical composition of the Sun, light bulbs, etc.
> The properties of Fresnel lenses, prisms, diffraction gratings, and light scattering
References and Links
(1) "What is Spectroscopy?" (Univ. of Arizona) : http://loke.as.arizona.edu/~ckulesa/camp/spectroscopy_intro.html
(2) "Spectroscopy" (Wikipedia): http://en.wikipedia.org/wiki/Spectroscopy
(3) Lesson plans and resources about spectroscopy (Cornell Univ.): http://www.lepp.cornell.edu/Education/TeacherResources.html
(4) 55 Lesson plans on Spectroscopy! (from Teacher Planet): http://www.lessonplanet.com/search?grade=all&keywords=spectroscopy&media=lesson&rating=3&search_type=related