CH 9 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. Differentiating between the two types

MECHANICAL WAVES Fill in the left side of the concept map Require a medium!! 2 types - Longitudinal & Transverse Examples: Longitudinal: sound, spring waves Transverse: water waves, some seismic waves

ELECTROMAGNETIC WAVES Fill in the right side of the concept map 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.)

Mechanical waves Longitudinal vs Transverse (diff between L & T) Longitudinal/compressional Waves   particle motion     wave motion   Label the wave in your notes You can conclude after watching this video that the particles in the medium of a longitudinal wave move (parallel or perpendicular) to the motion of the wave.

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

trough amplitude crest Mechanical waves Longitudinal vs Transverse Transverse Waves wavelength wave motion particle motion (turn off sound) Particles in a transverse wave move (parallel or perpendicular) to the wave motion. Rest Position

Parts of a Transverse 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

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

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: vUnit: 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 10 8 m/s (186,000 mi/s) in a vacuum.

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

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? DataFormulaWorkAns

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? DataFormulaWorkAns

9.3 Wave Behavior All electromagnetic waves travel at the speed of light in empty space (C). C = 3.0 X 10 8 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

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.lenses 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.