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

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

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: c/index.html Particle model: Electrons gain energy and “jump” to another level; when they fall back, they give off energy as light energy

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 videoEM video

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

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

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

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 wavelengthViolet = shorter w.l.

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

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

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

Refraction Bending of Light due to change in speed –M–MUST enter at an angle to “bend” –L–Light traveling from less dense to more dense, slows down and bends toward “normal” –L–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 Normal Less Dense

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

More Refraction: Bending and separating light YHave you seen ROY G. 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

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

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

Colors Light can be 1.transmitted through an object, 2.reflected, 3.or absorbed White: all the colors of the spectrum are reflected Black: all the colors are absorbed; the absence of color

How we see

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