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A “Light” Day of Notes. Maxwell’s Equations. J. C. Maxwell developed 4 equations which govern all of electricity and magnetism. These 4 equations make light work. You do not need to know these. Spectrum. - PowerPoint PPT Presentation
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A “Light” Day of Notes
Maxwell’s EquationsJ. C. Maxwell developed 4 equations which
govern all of electricity and magnetism.These 4 equations make light work.You do not need to know these.
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SpectrumJust like sound is classified according to its
pitch, there are different kinds of light, classified by their frequency.
The speed of light is constant.*Therefore, a certain frequency of light will
always have the same wavelength.We can also classify light by wavelength.
Electromagnetic Spectrum
RadioLowest Frequency EM
waves
AM (up to ~1 MHz)FM (90~100 MHz)Shortwave (in between)
VHF (TV)UHF (TV)Cell Phone reception
Radar
Microwave (-wave)The Gigahertz (GHz)
rangeWavelength in cm.Microwave ovens
operate at 2.45 GHzThis is a special
frequency to cause resonance in water
Infrared (IR)Wavelength in
“micrometers” (m)Most commonly referred
to as heatHot objects radiate their
thermal energy away.Up to a few hundred
degrees, the radiant energy is in the IR range
If we could see IR light, we would all shine brightly
More Infrared
VisibleThe light we can seeA tiny portion of the EM
spectrum
Red ( = 700 nm)OrangeYellowGreenBlueIndigoViolet ( = 450 nm)
Ultraviolet (UV)Wavelength as low as 10
nm
Used to kill germsBlack LightsThe part of sunlight that
causes sunburn and skin cancer
Partially blocked by the ozone layer
X-RayThese can be useful, but
also dangerousWavelength between 10
nm and 10 pmThat is from 10 billionths of a meter to 10 trillionths of a meter
Gamma Ray ( ray) < 10 pm
High energyDangerousRemember Gamma
radiation from last semester
PracticeWhat is the wavelength of AM radio wave
960 kHz?f = 960,000 Hzc = 3 × 108 m/s = c/f = 3 × 108 m/s ÷ 960,000 Hz = 312 m
PracticeWhat is the frequency of a “shortwave” radio
wave 120 meters long? = 120 mc = 3 × 108 m/sf = c/f = 3 × 108 m/s ÷ 120 mf = 2,500,000 Hz = 2,500 kHz = 2.5 MHz
PracticeWhat is the wavelength of an FM radio wave?
These waves are approximately 100 MHz (100 × 106 Hz).f = 100,000,000 Hzc = 3 × 108 m/s = c/f = 3 × 108 m/s ÷ 100,000,000 Hz = 3 m
PracticeWhat is the wavelength of a microwave in a
microwave oven? These waves are 2.45 GHz (2.45 × 109 Hz).f = 2,450,000,000 Hzc = 3 × 108 m/s = c/f = 3 × 108 m/s ÷ 2,450,000,000 Hz = 0.12 m = 12 cm
Conclusion -- Quiz Wed. (4/29)Electromagnetic
Spectrum
RadioMicrowaveInfraredVisible
Roy G BivUltravioletX RayGamma Ray
Visible Spectrum
RedOrangeYellowGreenBlueIndigoViolet