Light and the EM Spectrum
• The terms light, radiation, and electromagnetic wave can all be used to explain the same concept
• Light comes in many forms and it took physicists some time to realize that x-rays, visible light, radio waves, etc. are all the same phenomena
Jupiter seen at different wavelengths of light
Light as a Wave• One way to think about
light is as a traveling wave
• A wave is just a disturbance in some medium (water, air, space)
• A wave travels through a medium but does not transport material
• A wave does carry energy
Wave TerminologyReview• Wavelength - distance between two like points on the wave• Amplitude - the height of the wave compared to undisturbed state• Crest –the top most part of the wave OR point that exhibits Max + displacement• Trough –the bottom most part of the wave OR point that exhibits Max -
displacement
Wave Terminology
• Period - the amount of time required for one wavelength to pass • Frequency - the number of waves passing in a given amount of time
OR cycles/sec
frequency= 1/period period =1/frequency
Wavelengths of Light - Visible• What we see as white light is
actually made up of a continuum of components
• Traditionally, we break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV)
• There is actually a continuous transition of color, each with its own wavelength and frequency
Wavelengths of Light - Visible• Red light has an approximate wavelength of 7.0 x 10-7 m and a
frequency of 4.3 x 1014 Hz
• Violet light has an approximate wavelength of 4.0 x 10-7 m and a frequency of 7.5 x 1014 Hz
The Electromagnetic Spectrum• Human eyes are only able to process information from the visible
part of the spectrum• A radio wave has a wavelength close to the scale of a football field or
large building• Gamma-rays have a wavelength close in scale to a subatomic particle
or atomic nucleus
All EM radiation travels at the speed of light! ! = 2.99 �108 "⁄#