Chapter 25

Vibrations and Waves

Wave: a disturbance that transfers energy from place to place

Vibration: a repeated back and forth or up and down motion

The motion is the wave!

Vibration of a Pendulum

Period: the time of the back and forth swing

sine curve:

crest: the high point of a wave

trough: the low point of a wave

amplitude: the distance from the midpoint to the crest (or trough)

wavelength: the distance from the top of one crest to the top of another (l)

frequency: how often a vibration occurs

- measured in hertz (Hz)

frequency = 1/period

period = 1/frequency

The speed of a wave depends on the medium through which the wave moves

wave speed = wavelength X frequency

v = lf

transverse wave: a wave with vibration at right angles to the direction the wave is traveling

ex. string instruments, electromagnetic waves

longitudinal waves: a wave in which the vibration moves in the same direction as the wave

ex. sound waves

interference: two or more waves that arrive in a region at the same

time

constructive interference: one wave crest overlaps with another wave crest

result: bigger amplitude

destructive interference: one wave crest overlaps with the trough of another

result: cancellation (no wave)

Doppler Effect: the apparent change in frequency due to the motion of the source

the greater the speed of the source, the greater the Doppler Effect will be

ex. pitch of a car moving towards you, police radar

Doppler Effect also occurs for light

•used in astronomy calculations

What is Sound?

Sound is a disturbance that travels through medium as a longitudinal wave.

pitch: how high or low a sound seems

high pitch high frequencylow pitch low frequency

Most people can hear pitches with frequencies from

about 20 – 20,000 Hz

infrasonic: sound waves below 20 Hzex. elephants, whales

ultrasonic: sound waves above 20,000 Hz

ex:Dolphins and batsSonarMedical uses

Speed of Sound

depends on the elasticity, density and temperature of the medium

average speed of sound at room temperature: 340 m/s

elasticity: the ability of a material to bounce back after being disturbed

density: how close the particles are to each other

resonance: occurs when the frequency of a forced vibration on an object matches the natural frequency; an increase in amplitude occurs

beat: the periodic variation in the loudness of a sound

Occurs when two tones of slightly

different frequency are

sounded together.

Light

Speed of light = 300,000,000 m/s

ORabout 187,500 mi/s

f.y.i

A space shuttle travels at a rate of about 5 mi/s

light year: distance light travels in one year

electromagnetic wave: a transverse wave that is partly electric and partly magnetic

visible light: light you can

see

ROY G BIV

Most materials absorb some frequencies and reflect the rest.

The color you see is the light that is reflected.

Ex. If an object reflects red light

but absorbs all other frequencies,

then the object appears red.

If an object absorbs all

frequencies of light, then it

appears black.

If an object reflects all frequencies, then it appears white.

An object can only reflect frequencies

that are present in the

illuminating light.

Ex. Incandescent light is richer in frequencies

toward the lower end of the spectrum,

therefore, objects appear to be more red

Ex. Fluorescent lights tend to be richer in frequencies

toward the higher end of the spectrum, therefore,

objects appear more blue.

Together, all of the colors of the visible spectrum make white light (ex. sunlight)

White light also results from the

combination of red, green and blue.

What happens when certain

waves of visible light are

combined?

primary colors of light: red, green and blue

red + green = yellow

red + blue = magenta

green + blue = cyan

Mixing pigment is different than mixing light!!!

As pigments are added together, fewer colors of light are reflected and more are absorbed.

primary colors of pigment: cyan, yellow, magenta

http://www.youtube.com/watch?v=He0lkmbQGkI

Reflection: the bouncing back of a wave

MirrorsA plane (flat) mirror produces an image that is right side up and the same size as the object being reflected

virtual image: an upright image formed where rays of light appear to meet

real image: an inverted image where rays of light meet

Concave mirror: a mirror with a surface that curves inward like the inside of a bowlcan form either virtual or real images

ex. make up mirrorobjects appear bigger

Convex mirror: a mirror with a surface that curves outwardimages are always virtual

ex. passenger side view mirror

objects appear smaller

Refraction: the bending of waves as they enter a new medium

lens: a curved piece of glass or other transparent material that is used to refract light

concave lens: lens that is thinner in the center than at the edgesalso called divergent lensalways produces a virtual image

objects appear smaller

convex lens: lens that is thicker in the center than at the edges also called convergent lenscan produce a real or virtual image, depending on the position of the object

Objects can appear bigger or smaller