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!
• 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.
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!
> 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
> 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?
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
- 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.
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