The Study of Light

The Electromagnetic Spectrum  the arrangement of electromagnetic radiation according to wavelength.  includes gamma rays, X-rays, ultraviolet light, visible light, infrared radiation, microwaves, and radio waves.

The Nature of Light  Sometimes light behaves like waves, and other times like particles – it’s commonly referred to as a wavicle.  In the particle sense, light is thought to consist of small packets of information, called photons.  In the wave sense, you can use an analogy to waves on the ocean.

Wavelength and Frequency Wavelength (λ)is the distance from one wave crest to the next. Measured in nanometers (nm) 1 nm = 1 x 10-9 m = 0.000000001 m)

Wavelength and Frequency Frequency (f) is measured in cycles per second = Hertz (Hz) Number of waves that pass a given point in 1 second Look at this animation: http://www.ltscotland.org.uk/resources/s/sound/amplitude.asp?strReferringChannel=resources&strReferringPageID=tcm:4-248291-64 What is the relationship between wavelength and frequency?

Speed = wavelength x frequency Speed of Light All waves in the electromagnetic spectrum travel at the speed of light = 3 x 108 m/s.  The speed of light is a FUNDAMENTAL CONSTANT OF THE UNIVERSE.  Wavelength, frequency, and the speed of light are related by: Speed = wavelength x frequency Or c = λf

Visible Light  Visible Light is the narrow band of electromagnetic radiation that we can see.   Visible Spectrum Color Wavelength Red                 700 ‑ 650 nm Orange            649 ‑ 580 nm Yellow             579 ‑ 575 nm Green              574 ‑ 490 nm Blue                 489 ‑ 455 nm Indigo             454 ‑ 425 nm Violet              424 ‑ 400 nm  It consists of a range of waves with various wavelengths.

Invisible Light Invisible light refers to the portions of the EMS that humans cannot see with the unaided eye Includes Radio waves, Microwaves, Infrared, Ultraviolet, X rays, and Gamma Rays Radio, Micro-, and Infrared Waves all have wavelengths LONGER than red UV, X and Gamma Rays all have wavelengths SHORTER than violet

Light and Energy Light is actually a form of energy The amount of energy contained in the light is based on the frequency of the light Higher frequency light has more energy E = hf (h = Planck’s constant ) So…how are E and f related?

Formation of Spectra  A continuous spectrum is an uninterrupted band of color (all the colors of the rainbow.)  An absorption spectrum contains dark lines.  An emission spectrum contains bright lines.

Spectroscopy  Spectroscopy is the study of light as a function of wavelength that has been emitted, reflected or scattered from a solid, liquid, or gas.  Spectrometers are in use in the laboratory, in the field, in aircraft (looking both down at the Earth, and up into space), and on satellites.

Types of Spectroscopy There are as many different types of spectroscopy as there are energy sources! Here are just a few examples: Astronomical Spectroscopy Energy from celestial objects (such as stars) is used to analyze their chemical composition, density, temperature, and other characteristics. Infrared Spectroscopy The infrared absorption spectrum of a substance is sometimes called its “molecular fingerprint.” Frequently used to identify materials. Raman Spectroscopy Raman scattering of light by molecules may be used to provide information on a sample's chemical composition and molecular structure.

Application to Earth Studies This is a mineral map, where each color is the identification of specific minerals through imaging spectroscopy analysis.

Application to Earth Studies The plot above shows how data from a Raman spectrometer can be used to identify the chemical composition of minerals.

Application to Earth Studies Astronomers study stellar spectra in order to determine the chemical composition of stars. Every star in the sky has its own unique spectra making its identification kind of like finger printing stars.

http://www.colorado.edu/physics/2000/quantumzone/index.html