Physics Unit 3: Light

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Last updated 12:50 AM on 4/11/26
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10 Terms

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Electromagnetic waves

Electric and magnetic fields are perpendicular to each other and to the direction of motion of the wave

<p>Electric and magnetic fields are perpendicular to each other and to the direction of motion of the wave</p>
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Electromagnetic Spectrum, from low frequency (long wavelength) to high frequency (short wavelength)

Radio waves, microwaves, infrared, (visible light), Ultraviolet, X-rays, gamma rays

<p>Radio waves, microwaves, infrared, (visible light), Ultraviolet, X-rays, gamma rays</p>
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EM Spectrum: colors

  • Red - lowest frequency and longest wavelength

  • Frequency increases as light goes through the colors: red, orange, yellow, green, blue, violet

  • Violet light has nearly 2x the frequency of red light, and half the wavelength

<ul><li><p>Red - lowest frequency and longest wavelength</p></li><li><p>Frequency increases as light goes through the colors: red, orange, yellow, green, blue, violet</p></li><li><p>Violet light has nearly 2x the frequency of red light, and half the wavelength</p></li></ul><p></p>
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Transparent

Glass blocks both infrared and ultraviolet, but it is transparent to visible light

<p>Glass blocks both infrared and ultraviolet, but it is transparent to visible light</p>
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Light through matter

Speed of light through different materials:

  • Vacuum - c = 300,000,000 m/s

  • Atmosphere - slightly less than c

  • Water - 0.75c

  • Diamond - 0.41c

  • Change in speed causes the path of light to change - refraction

  • Path can be altered by shape of the material (lenses)

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Opaque materials

Opaque - absorb light without re-emitting it

  • Matter converts light into random KE in the matter - into thermal energy

  • These materials become slightly warm

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Opaque materials - metals

Light shining on metal forces free electrons in the metal into vibrations that emit their own light as reflection

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Mirror vs White Paper

Mirror

  • The surface is flat at distance scales near or above the wavelength of light

  • Looks “shiny”, and you can see images in it

White paper

  • Surface is rough at distance scales near or above the wavelength of light

  • Most surfaces reflect this way

<p><u>Mirror</u></p><ul><li><p>The surface is flat at distance scales near or above the wavelength of light</p></li><li><p>Looks “shiny”, and you can see images in it</p></li></ul><p><u>White paper</u></p><ul><li><p>Surface is rough at distance scales near or above the wavelength of light</p></li><li><p>Most surfaces reflect this way</p></li></ul><p></p>
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Law of Reflection

Incident rays and reflected rays make equal angles with a line perpendicular to the surface, called the normal

Angle of incidence - the angle between the incident ray and the normal

Angle of reflection - the angel between the reflected ray and the normal

Angle of incidence = angle of reflection

<p>Incident rays and reflected rays make equal angles with a line perpendicular to the surface, called the <strong>normal</strong></p><p><strong>Angle of incidence </strong>- the angle between the incident ray and the normal</p><p><strong>Angle of reflection </strong>- the angel between the reflected ray and the normal</p><p>Angle of incidence = angle of reflection</p>
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Partial reflection

Some materials are not as rigid to light waves

  • When light shines perpendicularly on the surface of still water, about 2% of its energy is reflected and the rest is transmitted

  • When light strikes glass perpendicularly, about 4% of its energy is reflected

  • The rest is transmitted