Characteristics of Waves Chapter 15.2 Notes

Wave Properties There are several wave properties, such as amplitude, wavelength, period, and frequency Amplitude and wavelength are measurements of distance Period and frequency are measurements based on time These 4 properties can be used to describe and compare waves

Amplitude Amplitude is the greatest distance that particles are displaced from their normal resting positions In a transverse wave, the amplitude is the distance from the rest position to either the crest or trough An ideal transverse wave has the shape of a sine curve; it looks like an S lying on its side The larger the amplitude of a wave, the more energy it carries

Wavelength The distance from one crest to the next crest, or from one trough to the next trough, is called the wavelength In a longitudinal wave, the wavelength is the distance between two compressions or between two rarefactions Generally, the wavelength is the distance between any two successive identical parts of a wave Wavelength is represented by the Greek letter lambda, λ, and it is measured in meters The shorter the wavelength of a wave, the more energy it carries

Period and Frequency The period is a measurement of the time it takes for a wave to pass a given point The time required for one complete vibration of a particle in a medium In equations, the period is represent by the symbol T, and it is measured in seconds Frequency is a measurement of the vibration rate It is the number of wavelengths that pass a point in a given time interval The symbol for frequency is f, and it is measured in hertz (Hz) Frequency and period of a wave are related The more vibrations that are made in a second, the less time each vibration takes frequency=1/period; f=1/T

Wave Speed The speed of a wave is equal to wavelength divided by period, or to frequency multiplied by wavelength Measured in meters per second (m/s) Wave speed is equal to the distance an object travels divided by the time it takes to travel that distance Wave speed = wavelength/period v=λ/T Speed of a wave can also be calculated by multiplying wavelength by the frequency (period is the inverse of frequency) Wave speed = frequency x wavelength v = f x λ

Wave Speed and the Medium The speed of a wave depends on the medium In a given medium though, the speed wave is constant If a wave is moving through the air, it will have the same speed throughout If a wave is moving through water, it will have the same speed throughout A wave may have a different speed in air than it does in water

Kinetic Theory and Wave Speed The arrangement of particles in a medium determines how well a wave can travel through it Gases: molecules are far apart and move randomly; molecules must travel through a lot of empty space before it bumps into another molecule Waves do not travel very fast in gases Liquids: molecules are closer together and can slide past one another; vibrations in one molecule are easily transferred to another molecule Waves travel faster through water than they do through air Solids: molecules are even closer together and bound more tightly together Waves travel very quickly through most solids

The Electromagnetic Spectrum All electromagnetic waves in empty space travel at the same speed, known as the speed of light Speed of light, represented by the symbol c, is 3.00 x 10 8 m/s Visible light is light that our eyes can detect—in the range of 4.3 x Hz to 7.5 x Hz Differences in frequencies in visible light accounts for the differences in color that we see The full range of light at different frequencies and wavelengths is called the electromagnetic spectrum f x λ = c; frequency x wavelength = speed of light

Pitch and Frequency Imagine you are standing on the street as an ambulance rushes by—as the ambulance passes, the sound of the siren changes from a high pitch to a lower pitch Motion between the source of waves and the observer creates a change in observed frequency The pitch of a sound, how high or low it is, is determined by the frequency at which sound waves strike the eardrum in your ear A high-pitched sound is caused by sound waves of high frequency

Doppler Effect If an ambulance is moving towards you, the sound waves from the siren are compressed in the direction of motion Between the time that one sound wave and the next sound wave are emitted, the ambulance is moving forward The distance between wave fronts is shortened, though the wave speed remains the same Sound waves reach your ear at a higher frequency and they sound higher- pitched If an ambulance is moving away from you, the frequency at which the waves reach your ear is less, and you hear the sound of the siren at a lower pitch than you would if the ambulance were at rest The change in observed frequency of a wave is called the Doppler effect