light waves and color metro community college 9/19/2015
TRANSCRIPT
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Light Waves and Color
Metro Community College04/21/23
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Electromagnetic Waves• Maxwell predicted that
an electric dipole would transmit changing electric and magnetic fields if a changing current was sent back and forth along the dipole.
• His equations proposed that light traveled at the same speed in all reference frames.
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What is an electromagnetic wave? • Electromagnetic waves are transverse electric field
waves in phase with magnetic field waves that travel away from the source at the speed of light in the medium.
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What is the speed of an electromagnetic wave?
• The speed of light, c is 3 X 10-8 m/s. the speed of light in medium is c/n where n is the index of refraction of the material.
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What is the frequency of an electromagnetic wave?
• The speed of light for our calculations is 3 X 108 m/s.
• The formula is v = f• The formula for the
energy of an electro-magnetic quantum is E = hf where h = 6.626X10-34 J-s
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Wavelength and Color
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Transmission and Reception
Transmission• Long wave – dipole• AM Radio – AM transmitter
varying the amplitude by changing energy
• FM Radio – FM transmitter varying the frequency of each wave.
• TV – Medium is changing• Infrared-light-ultraviolet –
atom emission.
Reception• Radio wave – dipole• AM receiver – to speaker,
current varies with amplitude of wave.
• FM receiver – various frequency waves become speaker frequencies
• TV Medium is changing• Diodes in eye, cameras.
Chemical changes in film.
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Transmission and Reception
Transmission• Ultraviolet – Atomic and
accelerated electron emissions
• X-rays – emissions by accelerating electrons
• Gamma rays – emissions by nuclei
Reception• Molecules with proper
energy levels, skin cells, and etc.
• Radiographic Film, photo sensors
• Electron collisions in material
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Eye Perception of Light
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Reflection of Light
Types of Reflection• Diffuse• Specular• Diffraction• Thin Film
Images differ from each one type of reflection.
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Transmission of Light
Types of transmission• Diffuse
– Scattering– Frosted glass
• Direct – clear glass• Diffraction
• single slit
• Interference– – double slit– grating
• Thin film
Examples
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Transmission of Light
Types of transmission• Diffuse
– Scattering– Frosted glass
• Direct – clear glass• Diffraction
• single slit
• Interference– – double slit– grating
• Thin film
Examples
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Interference of Light Waves• The bright lines occur
where the light is in phase and the path difference is one wavelength.
• The dark lines occur where the light is in phase and the path difference is one-half wavelength.
• Path difference = d(y/x)• = d(y/x) => bright• /2 = d(y/x) => dark
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Diffraction and Gratings
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y/x = (w/2)//2
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Polarized Light• Polarized Light – has the electric field set in a
particular orientation. A second polarized can block the electric field completely.
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Color MixingSubtraction – Pigment mixing subtracts. Total subtraction gives black.
Addition – light mixing results in the addition of light. Total addition results in white
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Scattering
Noon sun has less dust to come through, so it is yellow.
Sunset sun is red because it passes through the most dust and all long wavelengths are scattered
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The short wavelength light (near the blue end of the spectrum) is scattered from the dust in the air.
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Birefringence• Certain materials polarize
light passing through them in proportion to the stress on the material.
• Stress test – by putting the materials between crossed polarizing lenses. Light that is polarized again by the material will pass through.
• Since the amount of polarization depends on the wavelength the light that passes through appears in different colors.
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Summary
• Electromagnetic waves• Wavelength and color• Interference of light waves• Diffraction and gratings• Polarized light
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