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Light

Light. Particles, Waves, and Its Uses Intro to light with Tim and Moby. Light: Wave or Particle? . It’s both wave and particle! Light Waves are transverse waves. Photons : individual particles of light Bundles or packages of light energy. What causes Light Waves?. Wave Model:

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Light

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  1. Light Particles, Waves, and Its Uses Intro to light with Tim and Moby

  2. Light: Wave or Particle? • It’s both wave and particle! • Light Waves are transverse waves • Photons: individual particles of light • Bundles or packages of light energy

  3. What causes Light Waves? Wave Model: Electrical fields move at right angles to a magnetic field (a transverse wave) So it’s Electro-magnetic No medium required to travel (light travels through the vacuum of space) Interactive e.m. wave model: http://www.olympusmicro.com/primer/java/electromagnetic/index.html Particle model: Electrons gain energy and “jump” to another level; when they fall back, they give off energy as light energy

  4. The sun • Gives off all forms of electromagnetic waves • Sometimes called radiation: (the waves “radiate” away from the sun’s source) • The speed of light is 300,000 km/second (186,000 miles/sec) in a vacuum ! (a million times faster than the speed of sound) • EM video

  5. Electromagnetic spectrum • All the waves and frequencies of light are arranged by their wavelengths • Long wavelength (low frequency) = Low energy • Short wavelength (Higher frequency) = higher energy • As the frequency increases, the wavelength decreases • Does this change the speed of light? NO! • speed= frequency x wavelength • So if frequency increases and wavelength decreases the speed DOES NOT CHANGE (still 300,000 km/ sec) • Example: EM waves from a cell phone are low frequency but long wavelengths. They still travel at close to 186,000 miles per second

  6. Radio waves • Radio waves: long wavelengths, low energy • Uses: Includes TV,AM,FM, Cell Phones, microwaves • Interference: must have on different wavelengths or signals would cause “destructive interference” • invisible

  7. Infrared • Infrared waves: “heat waves” • Invisible • Uses: • Thermograph • Remote controls • Warming foods (heat lamps at the buffet)

  8. Visible Light • Visible spectrum • It’s visible! Very small part of spectrum you can see • Colors: All the visible colors have a different wavelength • ROY G. BIV Red = longer wavelength Violet = shorter w.l.

  9. Ultraviolet • Ultraviolet • Wavelengths too short to see (invisible) • Burning rays of sun • Other uses: Irradiate meat, our goggles for sterilization • Makes Vitamin D for bone production

  10. X-rays Invisible High energy, high frequency Pass through skin but not more dense objects (bone, lead) Uses: pictures of bone, teeth Airport security X-Ray

  11. Gamma • Gamma rays • Invisible • Highest energy and frequency, shortest wavelength • Can pass through 10 ft of concrete • Uses: kill cancer cells Brainpop on spectrum

  12. Refraction Normal • Bending of Light due to change in speed • MUST enter at an angle to “bend” • Light traveling from less dense to more dense, slows down and bends toward “normal” • Light traveling from more dense to less dense medium, speeds up and bends away from “normal” • The density of the material changes the amount of refraction • As the angle of the light ray entering increases (angle of incidence), the emergent (exiting ray) increases too. • Let’s look at this in action Less Dense

  13. Examples of refraction 1. White light enters water • “Water” on the road on a hot summer day • Density differences from heated air molecules • Looking into water 2. Reflected light • Light bends away from “normal” as it leaves the water and speeds up

  14. More Refraction:Bending and separating light • Have you seen ROYG. BIV? • White (visible) light is made up of colors • Refraction causes light to bend and separate colors • Longer wavelengths (Reds) don’t bend as much • Shorter wavelengths (violets) bend the most

  15. Reflection review • Bouncing back of light is reflection • Law of Reflection: • Angle of incidence = angle of reflection • Plane mirrors (flat): image is same size, right side up, and left and right are reversed • Virtual image: not “real”, image appears behind the mirror

  16. More reflection • Concave mirrors: inward curving mirrors (“like a cave”) • Image is focused at a point: Focal Point • This is a real image • Image may be upside down; depends on angle of reflection • Convex mirrors: outward curve • Rays of light spread out so image is right side up and smaller than the object • Convex and concave illustration

  17. Colors • Light can be • transmitted through an object, • reflected, • or absorbed White: all the colors of the spectrum are reflected Black: all the colors are absorbed; the absence of color

  18. How we see

  19. Sometimes your eyes play tricks on you Stroboscopic Artefacts Are these lines parallel or not?

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