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Waves

Wave

• Rhythmic disturbance that carries energy through matter or space.

Types of Waves

• Mechanical Waves– Require a medium

• Electromagnetic Waves– Move because of an

electromagnetic force field; don’t need a medium.

Types of Mechanical Waves

• Transverse– Vibration is

perpendicular to the direction of wave movement

• Longitudinal– Vibration is parallel to

wave motion.

• Surface Waves– Have characteristics of

both

Wave Properties

• Amplitude– Displacement from position of rest– Depends on how wave is generated– More “work” gives a larger amplitude

Wave Properties

• Wavelength – Distance of one wave from similar points (crest to

crest or trough to trough)– Represented with λ

Parts of Longitudinal Waves

Wave Properties

• Period– The time it takes for one wavelength to pass– Represented with T, measured in seconds

Wave Properties

• Frequency– Number of oscillations the wave makes each second.– Measured in hertz (Hz)

f = 1T

Wave Properties

• Speed– Depends on the material the wave is traveling through– Speed = λf

Interference

• The result of having two waves in the same place at the same time

• Also known as superposition• The waves will either combine or cancel

each other out

Types of Interference

• Destructive Interference – amplitudes are displaced in opposite directions, so they cancel each other out when meeting.

• Constructive Interference – amplitudes in same direction; add together

Standing Waves

• When waves’ reflections interfere constructively with each other.– Node – doesn’t move at all– Antinode – sees the largest displacement

Resonance• the tendency of a system to oscillate with

greater amplitude at some frequencies than at others

http://www.youtube.com/watch?v=hiHOqMOJTH4http://www.youtube. com/watch?v=zpUL6sZs6J4http://www.youtube.com/watch?v=nO0bSSXmr1A

Sound

• Sound waves– Pressure variation transmitted through matter.– Speed depends on the material traveling through

Loudness

• Depends on the amplitude of the pressure wave.• Remember more amplitude = more energy

Pitch

• Related to the frequency of the vibration

http://www.youtube.com/watch?v=ngk-ECb8ccQ

Doppler Shift

http://www.youtube.com/watch?v=Y5KaeCZ_AaYhttp://www.youtube.com/watch?v=Djz_rtnXSfY

Doppler Effect in Light

Light

• We refer to light as the part of the electromagnetic spectrum that is visible to our eyes.

Electromagnetic Spectrum

• Visible light is only one small part of the broad spectrum of electromagnetic waves.

http://www.youtube.com/watch?v=UzI1z0u_700

Light

• What we see as “white light” is actually a combination of all colors at once.

Name that band and album.

Perceiving Colors

• The color you see on an object is actually being absorbed by the object – what reaches our eye is everything BUT that color.

Polarization

• Light (ER) vibrates in two directions. Polarizing filters reduce the motion in one of the directions.

Polarization

http://www.olympusmicro.com/primer/lightandcolor/polarization.htmlhttp://www.sunglasswarehouse.com/thesunauthority/polarization-test

Reflection

• Law of Reflection– Angle of Incidence equals Angle of Reflection

http://www.youtube.com/watch?v=LTWHxZ6Jvjs

Reflection

• Regular Reflection– Smooth Surface

Reflection

• Diffuse Reflection– Rough Surface– Light is scattered

Refraction

• The bending of light waves at a boundary between two different media

http://homepage.usask.ca/~dln136/refraction/pages/first_intro.htmlhttp://www.youtube.com/watch?v=Bf1k9-4bb4w

Angle of Refraction

• The angle that a refracted wave makes with the normal

Critical Angle

• The incident angle that will cause a reflected ray to lie along the boundary of a surface.

Total Internal Reflection

• Angle at which the ray is reflected back into the medium

Fiber Optic Cable

Mirages

Diffraction

• Bending of a wave around an obstacle

http://www.falstad.com/ripple/http://w ww.gcsescience.com/pwav44.htm

Dispersion

• The separation of light into its colors

Why is the Sky Blue?

Objects vs. Images

• Object – the source of diverging light waves

• Image – the light that is viewed

Plane Mirror

• Smooth flat surface

Virtual Image

• The point that the eye interprets the light rays as having come from

• In a plane mirror, the image is the same size and distance from the mirror as the object is.

Concave Mirrors

• Curved inward• Principle axis – straight line to the surface

at the center

Concave Mirrors

• Focal point – where the parallel rays meet after reflecting.– Remember: Angle of incidence equals angle

of reflection!

Concave Mirrors

• Focal length – distance from the focal point to the mirror

• Real Image – light rays actually converge at that point (not virtual). Projected image.

Concave Mirrors

• Magnification – the ratio of the size of the image to the size of the object.

• Inside the focal point – forms enlarged virtual images.

• Outside the focal point – forms smaller virtual images that are upside-down.

Convex Mirrors

• Spherical – reflects light from the outer surface.

• Rays always diverge – no real images produced.

Lenses

• Made of a transparent material with a refractive index greater than air.

• Remember:– Transparent – light goes

through uninterrupted (clear

glass)– Translucent – light goes

through, but is scattered so

image is not easily seen

(frosted glass)– Opaque – no light goes

through

Convex Lens

• Thicker at the center than at the edges– Also known as converging lens

Concave Lens

• Thinnest in the center– Also known as a diverging lens