Electromagnetic Spectrum

Electromagnetic Spectrum (EM Spectrum) is the entire range of light radiation from gamma rays to radio

waves.

James Clerk Maxwell made a unified theory to describe electricity and magnetism

in 4 equations. He predicted that EM waves exist and predicted the

speed of light.

• Electromagnetism: phenomena caused by electricity and magnetism together.

• Electromagnetic Waves: Electric and magnetic fields work together to create traveling waves.

Electromagnetic Spectrum• Gamma Rays 1019 Hz to ∞• X-Rays 1017 Hz to 1019Hz• Ultraviolet 7.5x1014 Hz to 1017 Hz• Visible Light 4x1014 Hz to 7.5 x 1014 Hz• Infrared 1011 Hz to 4x1014 Hz• Microwaves 108 Hz to 1012 Hz• Radio Waves 102 Hz to 108 Hz

Speed of Light “c”• Romer (1644-1710: Danish) measured orbital period of Io

around Jupiter and noted differences depending on where Earth was located. Deduced a speed of light.

• Fizeau (1819-1896: French) first measured speed of light with mirrors and a notched rotating wheel.

• Michelson (1852-1931:American) measured more accurately with an 8 sided rotating mirror and a stationary mirror set 35 km apart on Mt. Wilson and Mt. Baldy in Ca. (pg 622 in text)

Speed of Light “c”• Velocity = Frequency (s-1) * Wavelength (m)

• Speed of Light

• c = 299,792,458 m/s

• c ≈ 3.0 x 108m/s

c = ƒλ

Calculation

• Calculate λ of the spectrum…

Electromagnetic SpectrumGamma Rays 1019 Hz to ∞X-Rays 1017 Hz to 1019HzUltraviolet 7.5x1014 Hz to 1017 HzVisible Light 4x1014 Hz to 7.5 x 1014 HzInfrared 1011 Hz to 4x1014 HzMicrowaves 108 Hz to 1012 HzRadio Waves 102 Hz to 108 Hz

How does that work????

The Radio

AM Amplitude Modulation

FM Frequency Modulation

How does that work????Sound pressure waves (mechanical) →

microphone →

audio frequency (electrical) →

mixed with radio frequency (carrier) →

amplified → transmitted. (Text pg 626 fig 22-12)

Calculation

Page 630: Problems 11, 13 & 27