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 travelsElectromagnetic radiation travels ________________in a vacuum –or about 186,000miles/second This velocity has a symbol of?This velocity has a symbol of? Travels in rays… straight line from an origin.Travels in rays… straight line from an origin E8 m/s c

Visible Light A small slice of the EM spectrum can be detected by human eyes.A small slice of the EM spectrum can be detected by human eyes. Color is the brains code for the frequency of perceived light.Color is the brains code for the frequency of perceived light. Roy G. Biv – acronymRoy G. Biv – acronym On the left are low frequencies and long wavelengths. On the right are high frequencies and short wavelengthsOn 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 White is ALL colors of the VS (visible spectrum)

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 Color Objects of a particular color absorb all other colors except for the color they “normally” appear.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.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 An object’s color depends SOLELY on the color of light that is reflected off of it. White light (roygbiv) Green only is reflected Object looks green

Color # 3- Rules for Color An object’s color depends SOLELY on the color of light that is reflected off of it. No light is reflected, no light reaches the eye, so object appears black! The turtle absorbed red light Filtered red light

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. Materialn Vacuum Air Ice1.31 Water1.333 Ethyl Alcohol1.36 Crown Glass1.52 Zircon1.923 Diamond2.417 n = c/v 3.00 E8 m/s 2.29 E8 m/s 2.25 E8 m/s 2.21 E8 m/s 1.97 E8 m/s 1.56 E8 m/s 1.24 E8 m/s

Law of Reflection Establish “normal” – an imaginary perpendicular line to the surface of a reflective object. mirror normal Θ Angle of incidence i Θ r Angle of reflection =

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. dd

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

Perfect (specular) reflection Plane mirrors create perfect parallel reflection of rays. mirror

Focused reflection Concave and Convex Mirrors create focused reflections. They still obey the Law of Reflection. ConvexConcave Focal point

Mirrors and Reflection #4 enlarged Multiple normals, resulting in slightly different reflected angles

Refraction High frequencies are more affected by this phenomenon. Snell’s Law also predicts how much it will be bent in the equation… n i sinΘ i =n r sinΘ r 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 θ incidence is different than the θ refracted.

Refraction#2 Optical density of the material determines amount of “bending” Optical density low Optical density high Optical density low High O.D. = small Θ Low O.D. = larger Θ parallel

water air Actual fishVirtual fish

Lenses Lenses obey Snell’s Law by refracting light to a certain degree. Lens shape has the biggest effect on light behavior. Two types : ConcaveConvex

Renaissance Masters - Tracers???