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Electromagnetic Radiation … aka Light. The EM spectrum Not just the “light” we can see… Ranges from low frequency radio waves to high frequency x-rays Small window of frequencies called “visible light”. Light Properties: Review. Electromagnetic radiation travels

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Electromagnetic Radiation … aka Light

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Electromagnetic radiation aka light

Electromagnetic Radiation … aka Light

The EM spectrum

Not just the “light” we can see…

Ranges from low frequency radio waves to high frequency x-rays

Small window of frequencies called “visible light”

Light properties review

Light Properties: Review

  • Electromagnetic radiation travels

    ________________in a vacuum

    • or about 186,000miles/second

  • This velocity has a symbol of?

  • Travels in rays… straight line from an origin.

3.00 E8 m/s


Visible light

Visible Light

  • A small slice of the EM spectrum can be detected by human eyes.

  • Color is the brains code for the frequency of perceived light.

  • Roy G. Biv – acronym

  • On the left are low frequencies and long wavelengths. On the right are high frequencies and short wavelengths

    R O Y GB I V

Color 1 rules for color

Color # 1- Rules for Color

  • White is ALL colors of the VS (visible spectrum)

Color 1 rules for color1

Color # 1- Rules for Color

  • Black is the absence of all colors.

  • Black appears black because nothing is reflected from it… therefore the light energy is turned to heat!

Color 1 rules for color2

Color # 1- Rules for Color

  • Objects of a particular color absorb all other colors except for the color they “normally” appear.

  • Ex. Green plants absorb all colors (roybiv) and use these energy frequencies to produce sugar during photosynthesis…, except green… they reflect green.

Color 2 rules for color

Color # 2- Rules for Color

  • An object’s color depends SOLELY on the color of light that is reflected off of it.

Green only is reflected

White light (roygbiv)

Object looks green

Color 3 rules for color

Color # 3- Rules for Color

  • An object’s color depends SOLELY on the color of light that is reflected off of it.

Filtered red light

No light is reflected, no light reaches the eye, so object appears black!

The turtle absorbed red light

Velocity of light through other materials snell s law

Velocity of light through other materials – Snell’s Law

  • When light travels through substances, its velocity is effected.

  • The amount the speed is reduced is the optical density (n)

  • n = c / velocity in the substance

Find the v of each of these

Find the v of each of these.

n = c/v

Law of reflection

Law of Reflection

  • Establish “normal” – an imaginary perpendicular line to the surface of a reflective object.







Angle of incidence

Angle of reflection


Inverted images

Inverted images

  • Mirrors produce images which have an “apparent distance” equal to that of the real object is from the mirror.

  • Images are also “inverted”

  • Mirrors need not be the same size as the object to produce a full sized image.



Mirrors and reflection

Mirrors and Reflection

  • Light rays travel in parallel rays from a source to an object that reflects them.

  • A reflection can be “diffuse”, “perfect”, or “focused”

  • Mirrors create either perfect (specular) or focused reflections depending on their shape.

Diffuse reflection

Diffuse Reflection

  • The rays are scattered in different directions. This is the way we see most objects in everyday life.

Perfect specular reflection

Perfect (specular) reflection

  • Plane mirrors create perfect parallel reflection of rays.


Focused reflection

Focused reflection

  • Concave and Convex Mirrors create focused reflections. They still obey the Law of Reflection.

  • ConvexConcave

Focal point

Mirrors and reflection 4

Mirrors and Reflection #4


Multiple normals, resulting in slightly different reflected angles



  • High frequencies are more affected by this phenomenon.

  • Snell’s Law also predicts how much it will be bent in the equation…

    ni sinΘi =nrsinΘr

  • n = optical density or Index of refraction.

Refraction 1


When light changes the material in which it travels, changes in velocity cause a change in direction. The θincidence is different than the θrefracted.

Refraction 2


Optical density low

Optical density high

Optical density low

Optical density of the material determines amount of “bending”


High O.D. = small Θ

Low O.D. = larger Θ

Electromagnetic radiation aka light



Virtual fish

Actual fish



  • Lenses obey Snell’s Law by refracting light to a certain degree.

  • Lens shape has the biggest effect on light behavior.

  • Two types :



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