Chapter 11 Waves and Wave properties

What is a wave? A wave is a disturbance that carries energy through matter or space

Waves Waves that require a medium are called mechanical waves Electromagnetic waves, also called light waves, are the only waves that do not require a medium

Electromagnetic Waves Light waves consist of changing electric and magnetic fields in space Examples: UV, infrared, and visible light waves

Waves and energy We know that waves carry energy because they can do work The bigger a wave is, the more energy it carries A tsunami is a huge ocean wave, that can carry enough energy to cause extensive damage to coastal towns and shorelines

Energy and Waves Energy spreads out as a wave travels Waves are related to vibrations Most waves are caused by a vibrating object Vibrations involve transformations of energy

Transverse and Longitudinal Particles in a wave can either move up and down OR back and forth Waves are classified by the direction the particles move Transverse wave Longitudinal wave

When a crowd does “the wave” at a sporting event, they are performing as a transverse wave The wave moves in a circle around the stadium, but the people move up and down The motion of the particles in the medium is at a right angle to the motion of the wave as a whole Transverse Waves

Longitudinal Waves A longitudinal wave causes the particles of the medium to vibrate parallel to the direction the wave travels Example: Sound waves

Longitudinal Waves A longitudinal wave can be created by a slinky when the first coils of the slinky are vibrated horizontally.

Surface Waves Some waves are not longitudinal waves OR transverse waves These other waves are surface waves Water waves are surface waves Surface waves occur at the boundary between two different mediums, like the boundary between water and air

Characteristics of Waves All transverse waves, no matter their size or what medium they are traveling though, have similar shapes An ideal transverse wave has the shape of a sine curve

Amplitude in Transverse Waves Amplitude measures the amount of particle vibration The highest points on a transverse wave are called the crests The lowest parts on a transverse wave are called the troughs The greatest distance that particles in a normal medium move from their normal position when a wave passes is called the waves amplitude

Amplitude in longitudinal waves Longitudinal waves do not have crests and troughs because the particles do not move up and down A longitudinal wave has compressions and rarefactions instead The high and low points of a sine wave correspond with the compressions and rarefactions of a longitudinal wave

Comparing Waves

Wavelength The distance between any two successive identical parts of a wave is called its wavelength So, in a transverse wave, the distance from the crest of a wave to the crest of the next wave, or the distance from the trough of one wave to the trough of another is an example of one wavelength

Wavelength In a longitudinal wave, the distance between two compressions or two rarefactions is one wavelength When used in equations, wavelength is represented by the Greek letter lambda, Because lambda is an SI unit, we label it in meters

Frequency The frequency of a wave is the number of full wavelengths that pass in a given time interval, its symbol is f and its units are Hertz It measures how rapidly vibrations occur in a medium

Hertz Hertz units measure the number of vibrations per second The SI unit Hertz is named after Heinrich Hertz, who in 1888, demonstrated that electromagnetic waves exist

Light Light comes in a wide range of frequencies and wavelengths Our eyes can detect light with frequencies ranging from 4.3 x Hz to 7.5 x Hz Light in this range is called visible light

Wave Speed Equation Wave speed equals frequency times wavelength Wave speed is represented with a V and is measured in m/s Frequency is represented by a f and is measured in Hertz Wavelength is represented by lambda and is measured in meters

V f Wavelength, labeled in meters Frequency, labeled in HZ Wave Speed, labeled in m/s

Characteristics of waves The speed of a wave depends on the medium it is traveling through In a given medium however, the speed of a wave is constant All electromagnetic waves in empty space travel at the same speed That speed is 3.0 x 10 8 m/s The speed of light is represented by the symbol c

Wave Interactions-- Reflection Reflection is what happens when a wave strikes a surface or boundary Waves reflect at a free boundary At a fixed boundary, waves reflect and turn upside down

Wave Interactions--Diffraction When waves pass the edge of an object or pass through an opening, such as a door, they are being bent This bending of waves around an edge is called diffraction The bending due to diffraction is not smooth it is abrupt and sudden, like changing directions while running down the hall

Wave Interactions-- Refraction When waves pass from one medium into another, they are bending due to a process called refraction This is why a spoon looks like it is broken into 2 pieces when it is resting in a glass half-full of water

Interference The combination of two or more waves that exist in the same place at the same time is called interference

Interference In constructive interference, amplitudes are added red = first wave blue = second wave green = resulting wave

Interference In destructive interference, amplitudes are subtracted red = first wave blue = second wave green= resulting wave

Standing Waves A standing wave is a form of a wave Standing waves DO NOT move through a medium Areas of no vibration are called nodes Midway between the nodes are points of maximum vibration. Areas of maximum vibration are called antinodes

Nodes and Antinodes

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