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 full EM spectrum

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 "⁄#