CHAPTER 10 WAVES Section 10.1 Types of Waves What does a wave carry? How are waves generated? What is the difference between a transverse wave and a longitudinal waves? How do the particles in ocean waves move? Intro to Waves Clip 1
What is a wave? Wave- a disturbance that transmits energy through matter or space Energy may spread out as a wave travels. Waves are all around us: light from the stoplight ripples in a puddle of electricity flowing in wires radio and television and cell phone transmissions Waves Medium- the matter through which a wave travels Water Air Earth-seismic waves Mechanical wave- a wave that requires a medium through which to travel sound waves (air) water waves waves in a spring 2
Waves Electromagnetic wave-a wave caused by a disturbance in electric and magnetic fields Does not require a medium Also called a light wave can transfer energy through a vacuum can also transfer energy through a material medium Example: light waves through space, through air, through glass Waves transfer Energy A wave caused by dropping a stone in a pond might carry enough energy to move a leaf up and down several centimeters A tsunami is a huge ocean wave caused by earthquakes. A tsunami can carry enough energy to damage coastal dwellings. Animation 3
Vibrations and Waves Most waves are caused by vibrating objects. Electromagnetic waves may be caused by vibrating charged particles. Mechanical waves are caused by the vibration of particles within the medium. Vibrations and Waves Vibrations involve transformations of energy A wave can pass through a series of vibrating objects. The disturbance travels down the row as energy is transferred from one mass to another. 4
Waves Transverse wave Particles oscillate up and down about their equilibrium positions, perpendicular to the direction of wave propagation its oscillations perpendicular to the direction the wave moves Examples: light waves, water waves, all waves belonging to the electromagnetic spectrum Longitudinal wave Particles oscillate back and forth about their equilibrium positions, parallel to the direction of wave motion oscillations in the same direction as the wave moves Example: Sound waves longitudinal wave transverse wave Clip 5
Waves Properties Waves have crests and troughs or compressions and rarefactions. compressions: the crowded areas of a longitudinal wave rarefactions: the stretched-out areas of a longitudinal wave Do longitudinal wave have crest and troughs? Surface Waves In a surface wave, particles move in circles. Water waves are an example of surface waves. Surface waves occur at the boundary between two different media Ex: water and air 6
Section 10.2 Characteristics of Waves What are some ways to measure and compare waves? How can you calculate the speed of a wave? Why does the pitch of an ambulance siren change as the ambulance rushes past you? Wave Properties Crest-the highest point of a transverse wave Trough-the lowest point of a transverse wave Amplitude-the greatest distance that particles in a medium move from their normal position when a wave passes Rest position 7
Wavelength Wavelength-the distance between any two successive identical parts of a wave represented by the symbol l expressed in the SI unit meters (m) Amplitude and wavelength tell you about energy. larger amplitude = more energy shorter wavelength = more energy A Longitudinal Waveform A cycle consists of one compression and one expansion of the particles of the medium. Particles of medium then return to their equilibrium positions 8
A Transverse Waveform A cycle consists of one crest and one trough. crest wavelength, l amplitude trough wavelength, l equilibrium position Your Turn 9
Period Period-the time required for one full wavelength to pass a certain point the time that it takes a complete cycle or wave oscillation to occur represented by the symbol T expressed in the SI unit seconds (s) Frequency frequency: the number of cycles or vibrations per unit of time; also the number of waves produced in a given amount of time represented by the symbol f expressed in the SI unit hertz (Hz), which equals 1/s 10
Frequency The frequency and period of a wave are related. The frequency is the inverse of the period. 1 frequency, or f 1/ T period What is the frequency in the diagram? f = 0.5 Hz What is the formula if you re looking for period? Period= 1/frequency Calculating Wave Speed Wave speed-the speed at which a wave passes through a medium Wave speed equals frequency times wavelength. Wave speed= frequency x wavelength V= f x Wave speed = v f= 1 T f V Wavelength = Period= T Frequency= f T= 1 f 11
Practice Problem: Wave Speed 1. The musical note A above middle has a frequency of 440 Hz. If the speed of sound is known to be 350 m/s, what is the wavelength of this note? ` f = 440 Hz v = 350m/s =? = v/f = 350 m/s 440 Hz = 0.80 m 2. A certain FM radio station broadcasts electromagnetic waves at a frequency of 9.05 x 10 7 Hz. These radio waves travel at a speed of 3.00 x 10 8 m/s. What is the wavelength of these radio waves? f = 9.05 x 10 7 Hz v = 3.00 x 10 8 m/s =? = v/f = 3.00 x 10 8 m/s 9.05 x 10 7 Hz = 3.31 m Practice Problem: Wave Speed 3. The average wavelength in a series of ocean waves is 15.0 m. A wave crest arrives at the shore on average every 10.0 s, so the frequency is 0.100 Hz. What is the average speed of the wave? f =.100Hz v =? = 15.0 m v = x f v = 15.0 m x.100 Hz v =1.5 m What is the period? T= 1/f T= 1/(.100Hz) T= 10 s 4. Yellow light with a wavelength of 5.89 x 10-7 m travels trough quartz glass with a speed of 1.94 x 10 8 m/s. What is the frequency of the light? f =? v = 1.94 x 10 8 m/s = 5.89 x 10-7 m f = v/ f = 1.94 x 10 8 m/s / 5.89 x 10-7 m f = 3.29 x 10 14 Hz What is the period? T= 1/f T= 1/(3.29 x 10 14 Hz) T=3.04 x 10-15 s 12
Practice Problems: Wave Speed 5. Waves in a lake are 6 m apart and pass a person on a raft every 2 s. What is the frequency? f =? t= 2s f = 1/ T f = 1/ 2 f = 0.5 Hz What is the speed of the wave? f = 0.5 Hz v =? = 6 m 6. A drum is struck, producing a wave with a wavelength of 1.1m and a speed of 2.42 x 10 4 m/s. What is the frequency of the wave? f =? v = 2.42 x 10 4 m/s = 1.1m What is the period? v = 6 m x 0.5 Hz f = v/ v = 3 m/s f = (2.42 x 10 4 m/s) / 1.1m f= 22000 Hz T= 1/f T= 1/22000 Hz T= 4.55 x 10-5 s Wave Speed The speed of a wave depends on the medium Greatest in solids and least in gases Kinetic theory explains differences in wave speed Light has a finite speed Speed of light: c = 3 x10 8 m/s 3 x10 8 m/s or 186,000 mi/s 13
Wave Speed Ranges of waves from lowest to highest are: radio waves, microwaves, infrared waves, visible light, ultraviolet light, X-rays, and gamma rays The full range of light frequencies is called the electromagnetic spectrum Doppler Effect Pitch is determined by the frequency of sound waves. The pitch of a sound =how high or low it is A higher-pitched sound is caused by sound waves of higher frequency. Frequency changes when the source of waves is moving Ex. Siren moving toward you sounds different than a siren moving away from you Doppler effect occurs for light and other type of waves as well 14
Doppler Effect Doppler effect-an observed change in the frequency of a wave when the source or observer is moving A sound wave frequency change is noticed as a change in pitch. The Doppler effect occurs for many types of waves, including sound waves and light waves. Video Clip Section 15.3 Wave Interactions How do waves behave when they hit a boundary, when they pass around an edge or opening, and when they pass from one medium to another? What happens when two or more waves are in the same location? How does a standing wave affect the medium in which it travels? 15
Wave Interactions Reflection Diffraction Refraction R Wave Interactions Waves bend when they pass from one medium to another at an angle. Waves will experience : Reflection Diffraction Refraction 16
Reflection Reflection the bouncing back of a wave as it meets a surface or boundary Examples: The reflection of light waves in a lake can create a mirror image of a landscape. Water waves are reflected when they hit the side of a boat. Diffraction Diffraction the bending of a wave as it passes an edge or an opening Examples: Water waves diffract around a block in a tank of water. Sound waves passing through a door diffract. 17
Refraction Refraction the bending of waves as they pass from one medium to another All waves are refracted when they pass from one medium to another at an angle. Interference Interference- the combination of two or more waves that exist in the same place at the same time Two types Constructive interference Destructive interference 18
Constructive Interference Waves combine without any phase difference Waves combine to form a bigger wave Increases amplitude Wave Addition Amplitude ~ Intensity 19
Destructive Interference Waves combine differing by multiples of 1/2 wavelength waves combine to form a wave smaller than the largest of the original waves Decreases amplitude Wave Subtraction 20
Interference Interference of light waves creates colorful displays Ex. Rainbows, oil in water, soap bubbles Interference Interference of sound waves produces beats 21
Standing Waves Standing waves-wave caused by interference that shows some regions of no vibrations Does not move along the medium Standing waves have nodes and antinodes Nodes Each loop of a standing wave is separated by a point Nodes have no vibrations Nodes are where the crests of the original waves meet the troughs of the reflected wave (destructive interference) Standing Waves Antinodes lie midway between the nodes point of maximum vibration form where the crests of the original waves line up with the crests of the reflected waves (constructive interference) Standing waves can have only certain wavelengths 22