# CH 8 Waves.

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CH 8 Waves

A WAVE is: a disturbance that transmits energy through matter or space in a regular pattern. Most waves are caused by… vibrating matter or particles. A medium is: the matter through which a wave travels; i.e. water, air Two types of waves, mechanical and electromagnetic.

MECHANICAL WAVES 2 types - Longitudinal or transverse Examples:
Require a medium!! 2 types - Longitudinal or transverse Examples: Longitudinal: sound, spring waves Transverse: water waves, some seismic waves Turn the page and forget about Electromagnetic waves, we will get back to them.

Longitudinal (compressional)
  particle motion     wave motion  

Particle Movement and Parts of a Longitudinal wave
Particles in the medium move parallel to the direction of the waves. The dense areas are called compressions. The less dense areas are rarefactions. Wavelength is measuring from compression to compression or rarefaction to rarefaction

Longitudinal Waves

Parts of a Transverse Wave
crest wavelength amplitude trough

Transverse Particles in the medium move perpendicular to the direction of the waves. wave motion particlemotion

Parts of a Wave Crest: the highest point (top) of a transverse wave.
Trough: the lowest point (bottom) of a transverse wave. Wavelength: the distance from any point on a wave to the same point on the next wave. (ex: crest to crest) Amplitude: the height measured from the resting position.

Motion of a Duck on a Wave

Water Wave

Seismic waves are transverse.

ELECTROMAGNETIC WAVES
(Turn back to page 1 to Complete the chart) Do not require a medium!! (Can travel in a vacuum like outer space.) 7 types of Electromagnetic Waves- radio waves, microwaves, infrared rays, visible light, ultraviolet, x-rays, gamma rays Modeled as transverse motion. (So they travel like ocean waves.)

Electromagnetic Waves Return back to the bottom of page 2

8.2 Wave Properties and Measurements
AMPLITUDE Not only is it the height of a wave but it measures the amount of energy in a wave. Greater amplitude = more energy.

WAVELENGTH PERIOD Symbol: Greek letter lambda, λ Tool: meterstick
Unit: meter (m) PERIOD Time it takes for a full wavelength to pass. Symbol: T Tool: stopwatch Unit: seconds (s)

FREQUENCY The rate at which waves pass (the # of full wavelengths that pass a point in 1 second). Symbol: f Unit: Hertz (Hz) 1 Hertz = 1 vibration per second Frequency is the inverse period 1 / P

WAVE SPEED How fast a wave moves. Symbol: v Unit: m/s
Wave speed is determined by the medium. Generally, waves pass through solids faster b/c particles are closer and can pass vibrations to each other more quickly.

WAVE SPEED cont. EX: Speed of sound in air: 340 m/s
in water: 1490 m/s in iron: 5000 m/s An exception is light, which travels slower in a medium than in empty space (vacuum). All electromagnetic waves travel at a speed of 3.0 x 108 m/s (186,000 mi/s) in a vacuum.

Sound Waves

EQUATIONS v = f · λ f = v / λ λ = v / f v UNITS: λ = meters (m)
Wave speed = frequency times wavelength v = f · λ f = v / λ λ = v / f UNITS: λ = meters (m) f = Hertz (Hz) v = m/s v f λ

The string of a piano that produces the note middle C vibrates with a frequency of 264 Hz. If the sound waves produces have a wavelength of 1.30 m in air, what is the speed of sound in air? Data Formula Work Ans

A water wave has a speed of 1. 3 m/s
A water wave has a speed of 1.3 m/s. A person sitting on a pier observes that it takes 1.2 s for a full wavelength to pass the edge of the pier. What is the wavelength of the water wave? Data Formula Work Ans

8.3 Wave Behavior All electromagnetic waves travel at the speed of light in empty space. C = 3.0 X 108 m/s (186,000mi/s) Light travels slower through a medium.

The Doppler Effect An observed change in the frequency of a wave when the source or observer is moving. The sound waves’ frequency and pitch are higher as the ambulance moves toward A. The sound waves’ frequency and pitch are lower as the ambulance moves away from the observer. Closer waves = high frequency, high pitch Frequency and Pitch are directly related.

DOPPLER EFFECT Pitch of a sound is determined by the wave’s frequency

Auto Racing Sound waves from an approaching object are closer together than sound waves from the object when it is standing still. The speed of the approaching object determines how much closer the waves will be. The sound waves from an object going away are farther apart than the waves from the same object standing still. Again the speed of the object deter- mines how much farther apart the waves from the moving object are than those from the stationary object.  A race fan standing by the track hears a high-pitched sound as a car approaches which changes suddenly to a lower pitch as the car passes and begins to move away. The amount of change in pitch is determined by the speed of the car. Fans with perfect pitch can clock a car reasonably accurately by listening to the pitch change in the sound of the engine as the car passes them.

Reflection The bouncing back of a wave as it meets a surface or boundary

Reflection When a wave has a free boundary they reflect like the original wave When a wave has a fixed boundary they reflect upside down Free boundary Fixed boundary

Diffraction The bending of a wave as it passes an edge or an opening

Diffraction

Refraction The bending of waves as they pass from one medium to another

Refraction Each time a wave enters a new medium they bend

Refraction is the bending of a wave when it enters a medium where it's speed is different.
Refraction is responsible for image formation by lenses and the eye.

Types of Interference Constructive Destructive Light wave interference
Sound wave interference

Constructive Interference
When the crest of one wave overlaps the crest of another wave resulting in a new wave with an amplitude that is the sum (larger) of the 2 individual waves amplitudes. Resulting amplitude is larger.

Destructive Interference
When the crest of one wave overlaps the trough of another and the resulting wave’s amplitude is smaller than the original 2 wave’s amplitudes.

Light Interference Iridescence of peacock feathers is caused by light reflected from complex layered surface

Sound Interference – Interference of sound waves produce BEATS

White Noise????? Because white noise contains all frequencies, it is frequently used to mask other sounds. Example: If you are in a hotel and voices from the room next-door are leaking into your room, you might turn on a fan to drown out the voices.

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