Waves are for SURFING… yeah!

Copyright © 2008 Pearson Education Inc., publishing as Pearson Addison-Wesley

Waves are for SURFING… yeah!

Cayucos, CA

Monterey, CA


Get outta there

Ghost tree


If you double the wavelength l of a wave on a string, what happens to the wave speed v and the wave

frequency f?A. v is doubled and f is doubled.

B. v is doubled and f is unchanged.

C. v is unchanged and f is halved.

D. v is unchanged and f is doubled.

E. v is halved and f is unchanged.

Q15.1


If you double the wavelength l of a wave on a string, what happens to the wave speed v and the wave

frequency f?A. v is doubled and f is doubled.

B. v is doubled and f is unchanged.

C. v is unchanged and f is halved.

D. v is unchanged and f is doubled.

E. v is halved and f is unchanged.

A15.1


Which of the following wave functions describe a wave that moves in the –x-direction?

A. y(x,t) = A sin (–kx – wt)

B. y(x,t) = A sin (kx + wt)

C. y(x,t) = A cos (kx + wt)

D. both B. and C.

E. all of A., B., and C.

Q15.2


Which of the following wave functions describe a wave that moves in the –x-direction?

A. y(x,t) = A sin (–kx – wt)

B. y(x,t) = A sin (kx + wt)

C. y(x,t) = A cos (kx + wt)

D. both B. and C.

E. all of A., B., and C.

A15.2


A new swell

A swell arrived last night and the buoys indicated an 18 second period with 3m height. Sweet!! The wave velocity where the buoys are located is 28 m/s.

What is the amplitude, angular frequency, wavelength and wave number of the wave?

Write a wave function describing the wave.

What is the velocity of the buoy 5 s after the peak of the wave passes under it?

Rincon


The speed of a transverse wave

• In the first method we will consider a pulse on a string.

• Figure 15.11 will show one approach.


A wave on a string is moving to the right. This graph of y(x, t) versus coordinate x for a specific time t shows the shape of part of the string at that time.

At this time, what is the velocity of a particle of the string at x = a?

A. The velocity is upward.

B. The velocity is downward.

C. The velocity is zero.

D. not enough information given to decide

Q15.3

x

y

0a



At this time, what is the velocity of a particle of the string at x = a?





A15.3

x

y

0a



At this time, what is the acceleration of a particle of the string at x = a?

A. The acceleration is upward.

B. The acceleration is downward.

C. The acceleration is zero.


Q15.4

x

y

0a



At this time, what is the acceleration of a particle of the string at x = a?

A. The acceleration is upward.

B. The acceleration is downward.

C. The acceleration is zero.


A15.4

x

y

0a



At this time, what is the velocity of a particle of the string at x = b?





Q15.5

x

y

0b



At this time, what is the velocity of a particle of the string at x = b?





A15.5

x

y

0b


The speed of a transverse wave II

• What happens to wave velocity, frequency and wavelength of waves travelling up the rope?

A. v , f , l B. v , f , l C.v , f =, l D.v , f , l =

E. Not enough information


The speed of a transverse wave II

• Nylon rope is tied to a stationary support at the top of a vertical mine shaft 80 m deep. The rope is stretched taut by a 20 kg box of mineral samples at the bottom. The mass of the rope is 2 kg. The geologist at the bottom signals by jerking the rope sideways.

• What is the speed of the transverse wave on the rope?

• If the rope is given SHM with frequency 2 Hz, how many cycles (wavelengths) are there in the rope’s length?


The four strings of a musical instrument are all made of the same material and are under the same tension, but have different thicknesses. Waves travel

A. fastest on the thickest string.

B. fastest on the thinnest string.

C. at the same speed on all strings.


Q15.8


The four strings of a musical instrument are all made of the same material and are under the same tension, but have different thicknesses. Waves travel

A. fastest on the thickest string.

B. fastest on the thinnest string.

C. at the same speed on all strings.


A15.8


The speed of waves on a string and speed of sound

• A note on a bass guitar produces sound waves. The frequency of the string’s oscillations is 20 Hz and the wavelength was 10m. What happens to the velocity, frequency and wavelength of the waves when they leave the guitar and propagate through the air?

A. v , f , l B. v , f , l C.v , f =, l D.v , f , l =

E. Not enough information


When light passes from vacuum (index of refraction n = 1) into water (n = 1.333),

Q33.1

A. the wavelength increases and the frequency is unchanged.

B. the wavelength decreases and the frequency is unchanged.

C. the wavelength is unchanged and the frequency increases.

D. the wavelength is unchanged and the frequency decreases.

E. both the wavelength and the frequency change.


When light passes from vacuum (index of refraction n = 1) into water (n = 1.333),

A33.1

A. the wavelength increases and the frequency is unchanged.

B. the wavelength decreases and the frequency is unchanged.

C. the wavelength is unchanged and the frequency increases.

D. the wavelength is unchanged and the frequency decreases.

E. both the wavelength and the frequency change.


v = c v = c

• A light wave travels from vacuum, through a transparent material, and back to vacuum. What is the index of refraction of

this material? Explain


Wave intensity• Go beyond the wave on a string and visualize, say … a

sound wave spreading from a speaker. That wave has intensity dropping as 1/r2.


Thumping bassYou are 3m from your friend’s car, who is

pumping obnoxiously loud, bass-heavy music through his subwoofer-equipped car, causing the entire car to rattle. He yells to you that he’s got a 800W subwoofer in his car and its cranked to full volume. Unimpressed, you measure a peak sound intensity of 4.4 W/m2 on your handy Radioshack soundmeter. How many watts is your friend’s subwoofer putting out?

What is the sound intensity for your friend in the car, at 1 m away from the subwoofer?


The logarithmic decibel scale of loudness

• Our ears can comfortably hear sound over 12 orders of magnitude in intensity!


Thumping bassYour friend has fixed the “problem” with their

subwoofer and is now pumping 800W of obnoxiously loud, bass-heavy music through their subwoofer-equipped car, causing the entire car to rattle. If the bass note is vibrating at 40 Hz, what is the maximum displacement of air at 1 m away from the subwoofer?

How many dB’s is this?

Why does your friend have an 800W subwoofer instead of an 800W amplifier for all sound frequencies?


The Doppler Effect II—moving listener, moving source• As the object making the sound moves or as the listener

moves (or as they both move), the velocity of sound is shifted enough to change the pitch perceptively.


A. a higher frequency and a shorter wavelength.

B. the same frequency and a shorter wavelength.

C. a higher frequency and the same wavelength.

D. the same frequency and the same wavelength.

Q16.8

On a day when there is no wind, you are moving toward a stationary source of sound waves. Compared to what you would hear if you were not moving, the sound that you hear has






A16.8

On a day when there is no wind, you are moving toward a stationary source of sound waves. Compared to what you would hear if you were not moving, the sound that you hear has


On a day when there is no wind, you are at rest and a source of sound waves is moving toward you. Compared to what you would hear if the source were not moving, the sound that you hear has





Q16.9


On a day when there is no wind, you are at rest and a source of sound waves is moving toward you. Compared to what you would hear if the source were not moving, the sound that you hear has





A16.9


A double Doppler shift• What is the frequency of the 300 Hz siren that’s heard

by (a) a person in the warehouse and (b) in the police car as it travels towards the warehouse?


You are standing at x = 0m, listening to seven identical sound sources. At t = 0, all seven are at x = 343 m and moving shown below. The sound from all seven will reach your ear at t = 1s.

Rank in order, from highest to lowest, the seven frequencies f1 to f7 that you hear at t = 1s.

1234

567

50 m/s speeding up50 m/s, steady speed50m/s, slowing down

50 m/s speeding up50 m/s, steady speed50m/s, slowing downAt rest

Doppler shift from several sources

Waves are for SURFING… yeah!

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