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What is Light?

What is Light?. What is Light? Light is a kind of electromagnetic radiation. Light travels in transverse waves. Speed of Light (c) = 3.00 x 10 8 m/s (in a vacuum) That’s 186,000 miles per second.

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What is Light?

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  1. What is Light? • What is Light? • Light is a kind of electromagnetic radiation. • Light travels in transverse waves. • Speed of Light (c) = 3.00 x 108 m/s (in a vacuum) • That’s 186,000 miles per second At this speed light could travel the equivalent of 8 times around the world in one second!

  2. Light travels much faster than sound. For example: • Thunder and lightning start at the same time, but we will see the lightning first. • 2) When a starting pistol is fired we see the smoke first and then hear the bang.

  3. Practice Problem Ex. If a light wave has a frequency of 500,000 Hz, what is its wavelength? Given: F = 500,000 Hz λ = ? V = f λ 3.00 x 108 = 500,000 λ 600 m

  4. Electromagnetic Spectrum X-Rays Radiowaves Microwaves Ultra-violet GammaRays Infrared . Visible Light

  5. Radio Waves • Radio Stations, 2-way radio, remote controls, radar (navigation), listening devices (bugs) • Microwaves • Microwaves, Cellular phones, speed radars, Television, Ovens • Infrared • Movie – Predator, Police, Firemen, heating & air Electromagnetic Spectrum

  6. Electromagnetic Spectrum • Visible Spectrum – Light we can see • R OYGBIV • Largest to Smallest Wavelength. • Larger wavelength = Lower frequency = less energy • Shorter wavelength = Higher frequency = more energy

  7. UV light (Ultraviolet Light) • Sun, Tanning Beds, Black Lights • X - Rays • Medical x-rays, airport security, • Gamma Rays • Sterilizing Equipment, Cancer treatments, Electromagnetic Spectrum

  8. Short wavelength High frequency High energy Long wavelength Low frequency Low energy

  9. is the bending of the path of a light wave as it passes across the boundary separating two media. is caused by the change in speed experienced by a wave when it changes medium. Refraction

  10. When light travels from a less dense to • more dense medium (light slows down), • the ray is refracted toward the normal. • Example: light slows down when it passes from air into water • When light travels from a more dense • medium to a less dense medium (light speeds up), the ray is refracted away from the normal. • Example: light speeds up when passing from glass into air

  11. Index of refraction (n) Basically it says how hard it is for light to travel through a media. The higher the number the harder it is to travel. Index of refraction

  12. Snell’s Law: n1sin(q1) = n2sin(q2) • n1 = index of refraction of medium 1 • θ1= incident angle or θi • n2 = index of refraction of medium 2 • θ2=refracted angle or θr • To calculate: BE IN DEGREE MODE! Snell’s Law

  13. Practice A person is shinning a flashlight (through air 1.0) into an unknown medium (n2). The light enters at 28° to the normal line. It becomes 10 °within the 2nd medium. Calculate the index of refraction of the 2nd medium? 28o n1 = 1.0 air 10°o n2= ? 10o Snell’s Law Example

  14. Snell’s Law - Example n1 = 1.00 q1 = 28 ° q2 = 10 °θ n2 = unknown index • (1.00) sin(28) = n2 (sin 10) • 0.469 = n2 (0.174) • Divide by 0.174 • n2 = 2.70 • We can then check this value against the list of known refractive indexes and identify the material. n1sin(θ 1) = n2sin(θ 2)

  15. Index of refraction

  16. Given: ni = 1.00, nr = 1.33, θi = 45 ° Find θr Snell’s Law Example 45° • 1.00 * sine (45 °) = 1.33 * sine (θr) • 0.7071 = 1.33 * sine (θr) • 0.532 = sine (θr) • sine-1 (0.532) = sine-1 ( sine (θr)) • 32.1 ° = θr

  17. Index of refraction(n)=speed of light in a vacuum(c) speed of light in material (v) Index of refraction Another Equation … Practice Problem Calculate the speed of light in water. Water has an index refraction of 1.33. 1.33 = 3x108m/s n n =

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