Physics Exam 1

Mike is holding one end of a Slinky. His hand moves up and

down and causes a transverse wave to travel along the Slinky

away from him. Is the motion of Mike's hand a wave?

No, the motion of Mike's hand is not a wave because there is no traveling disturbance.

Jimmy and Jenny are floating on a quiet river using giant

doughnut-shaped tubes. At one point, they are 5.0 m apart when a

speed boat passes. After the boat passes, they begin bobbing up and

down at a frequency of 0.25 Hz. Just as Jenny reaches her highest

level, Jimmy is at his lowest level. As it happens, Jenny and Jimmy

are always within one wavelength. What is the speed of these waves?

2.5 m/s

A longitudinal wave with an amplitude of 0.02 m moves

horizontally along a Slinky with a speed of 2 m/s. What is the horizontal distance moved during each period of the wave?

0.04 m

A sound wave is being emitted from a speaker with a

frequency f and an amplitude A. The sound waves travel at a

constant speed of 343 m/s in air. What action would reduce the wavelength of the sound waves to one half of their initial value?

decrease the frequency to f /2

The tension of a guitar string in increased by a factor of 4. How

does the speed of a wave on the string increase, if at all?

The speed of a wave is increased to two times the value it had before the increase in tension.

A climbing rope is hanging from the ceiling in a gymnasium.

A student grabs the end of the rope and begins moving it back

and forth with a constant amplitude and frequency. A transverse

wave moves up the rope. What is true regarding the speed of the wave?

The speed of the wave increases as it moves upward.

When a wire is stretched by a force F, the speed of a

traveling wave is v. What is the speed of the wave on the

wire when the force is doubled to 3F?

v times the square root of 3

A radio station broadcasts its radio signal at a frequency of

101.5 MHz. The signals travel radially outward from a tower at

the speed of light. What equation represents this wave if t is expressed in seconds and x is expressed in meters?

y = 150 sin[(6.377 x 108)t − (2.123)x]

The equation for a certain wave is y = 4.0 sin [2pi(2.5t + 0.14x)]

where y and x are measured in meters and t is measured in seconds.

What is the magnitude and direction of the velocity of this wave?

18 m/s in the −x direction

Which one of the following statements correctly describes the wave given

as this equation: y = 3 sin ( -4x+2 ) , where distances are measured in cm and

time is measured in ms?

The wave is traveling in the +x direction with an amplitude of 3 cm and a wavelength of pi/2 cm.

Which one of the following correctly describes a wave described by y =

2.0 sin(3.0x − 2.0t) where y and x are measured in meters and t is measured

in seconds?

The wave is traveling in the −x direction with a frequency 4pi Hz and a wavelength pi/3 m.

While constructing a rail line in the 1800s, spikes were driven

to attach the rails to cross ties with a sledge hammer. Consider the

sound that is generated each time the hammer hits the spike. How

does the frequency of the sound change, if at al, as the spike is

driven into the tie?

The frequency of the sound increases as the spike is driven

In a classroom demonstration, a physics professor breathes in a small amount of helium and begins to talk. The result is that the professor's normally low, baritone voice sounds quite high pitched. What best describes this phenomena?

The wavelength of the sound generated in the professor's throat and mouth is only changed slightly, but since the speed of sound in helium is approximately 2.5 times larger than in air, therefore the frequencies generated are about 2.5 times higher.

Ethanol has a density of 659 kg/m3. If the speed of sound

in ethanol is 1162 m/s, what is its adiabatic bulk modulus?

8.9 x 10^8 N/m^2

Natalie is a distance d in front of a speaker emitting sound

waves. She then moves to a position that is a distance 2d in front

of the speaker. By what percentage does the sound intensity

decrease for Natalie between the two positions?

75%

A bell is ringing inside of a sealed glass jar that is

connected to a vacuum pump. Initially, the jar is filled with

air at atmospheric pressure. What does one hear as the air is

slowly removed from the jar by the pump?

The sound intensity gradually decreases

A sound level meter is used measure the sound intensity level. A sound

level meter is placed an equal distance in front of two speakers, one to the

left and one to the right. A signal of constant frequency may be sent to

each of the speakers independently or at the same time. When either the

left speaker is turned on or the right speaker is turned on, the sound level

meter reads 90.0 dB. What will the sound level meter read when both

speakers are turned on at the same time?

93.0 dB

A sound level meter is used measure the sound intensity level. A sound

level meter is placed an equal distance in front of two speakers, one to the

left and one to the right. A signal of constant frequency, but differing

amplitude, is sent to each speaker independently. When the left speaker is

turned on the sound level meter reads 85 dB. When the right speaker is

turned on the sound level meter reads 65 dB. What will the sound level

meter read when both speakers are turned on at the same time?

about 85 dB

Software is used to amplify a digital sound file on a computer

by 20 dB. By what factor has the intensity of the sound been

increased as compared to the original sound file?

100

Two stationary observers, Keisha and Trina, are listening to the sound from a

moving source. The sound from the source has a constant frequency fS and constant amplitude. As the source moves, Trina hears two different frequencies f1 and f2, where f1 > fS and f2 < fS. Keisha, who is not moving with the source, only hears one frequency, f. What best explains this situation?.

The source is moving along a circle and Keisha is at the center of the circle. Trina is outside the circle.

Hydrogen atoms in a distant galaxy are observed to emit light that

is shifted to lower frequencies with respect to hydrogen atoms here

on Earth. Astronomers use this information to determine the relative

velocity of the galaxy with respect to the Earth by observing how

light emitted by atoms is Doppler shifted. For the hydrogen atoms

mentioned, how are the wavelengths of light affected by the relative

motion, if at all?

The wavelengths of light would be longer than those observed on Earth

Give the equation of a wave that would undergo fully constructive interference with a wave described by y = 2.0 sin (3.0x - 2.0t) where y and x are measured in meters and t is measured in seconds?

y = -sin (-3.0x + 2.0t)

A radio station has a transmitting tower that transmits its signal (electromagnetic waves)uniformly in all directions on the west end of Main Street. They are considering building asecond, identical transmitter at the east end of Main Street, ten miles due east of the firsttransmitter. The same signal is to be broadcast at the same time from both towers. As youdrive ten miles east to west on Main Street, what would you hear as you listen to the radiostation broadcast from these two towers?

The signal alternates between increasing strength and decreasing strength as you drive the ten miles

Two identical speakers are emitting a constant tone that has awavelength of 0.50 m. Speaker A is located to the left of speaker B. At which locations would complete destructive interference occur?

3.75 m from speaker A and 2.50 m from speaker B

Two waves, A and B, are superposed. For which one of thefollowing circumstances will beats result?

A and B are waves with slightly differing frequencies, butotherwise identical

A transverse standing waves is present on a plucked guitarstring. What is the distance from the fixed end of a string to thenearest antinode?

wavelength / 4

Which one of the following statements is true concerning thepoints on a string that sustain a standing wave?

a) All points undergo motion that is purely longitudinal.

b) All points vibrate with the same energy.

c) All points vibrate with different amplitudes.

d) All points undergo the same displacements.

e) All points vibrate with different frequencies.

c

A rope of length L is clamped at both ends. Which one of thefollowing is not a possible wavelength for standing waves on thisrope?

a) L/2

b) 2L/3

c) L

d) 2L

e) 4L

e

Consider a wire under tension that is driven by an oscillator. Initially, thewire is vibrating in its second harmonic mode. How does the oscillation of thewire change as the frequency is slowly increased?

No standing wave may be observed until the frequency matches the thirdharmonic mode of the wire.

Why does a piano and a guitar playing the same musical note sound different?

The two instruments have the same fundamental frequency and thesame harmonic frequencies, but the amounts of each of theharmonics is different for the two instruments.

The sound emitted from a strummed guitar string is either aresonant frequency or one of its harmonics. Although the stringis not being driven at its resonant frequency, no non-resonantwaves are emitted. Describe why non-resonant waves are not heard

The non-resonant waves are too quickly damped out.

A soft drink bottle is 15 cm tall. Joey blows across that topof the bottle just after drinking the last of his drink. What is theapproximate fundamental frequency of the tone that Joeygenerates?

a) 230 Hz

b) 570 Hz

c) 680 Hz

d) 810 Hz

e) 1100 Hz

b

Which one of the following statements concerning standing waves within apipe open only at one end is true?

a) The standing waves have a fundamental mode have a shorter wavelength thanthat for the same tube with both ends open.

b) The standing waves must be transverse waves, since longitudinal waves could notexit the tube.

c) The standing waves have a greater number of harmonics than which occur for thetube when both ends are open.

d) The standing waves have fewer harmonics than which occur for the tube whenboth ends are open.

e) The standing waves have a fundamental mode with a smaller frequency than thatwhich occurs when both ends of the tube are open.

e

Given that the first three resonant frequencies of an organpipe are 200, 600, and 1000 Hz, what can you conclude aboutthe pipe?

the pipe is closed at one end and has a length of 0.475 m.

transverse wave vs longitudinal waves

transverse: compressed and stretched regions

longitudinal: up and down waves (what u typically think of when u think of waves)

are water waves transverse or longitudinal?

both

Periodic Waves

cycles/ patterns produced over and over again by the source

Amplitude

maximum exercusion of a particle of the medium from the particles undisturbed position

Wavelength

horizontal length of 1 cycle of the wave

period

time to complete 1 cycle

Frequency

related to the period and has units Hz

the speed at which the wave moves to the right depends on:

how quickly one particle of the string is accelerated upward in response to the net pulling force

are individual air molecules carried along the wave?

No

Pure tone

sound with a single frequency

Pitch

subjective quality in which the brain interprets the frequency

Loudness

attribute of sound that depends primarily on the pressure amplitude of the wave

Power

amount of energy transported per second

Sound Intensity

the power that passes perpendicularly through a surface divided by the area of that surface

Threshold of Hearing

for a 1000Hz tone, the smallest sound intensity that the human ear can detect is about 1 x 10^-12 W/m^2

Decibel (dB)

measurement unit used when comparing 2 sound intensities together

Doppler Effect

change in frequency/pitch of the sound detected by an oberserver because the sound source and observer have different velocities with respect to the medium of sound propogation

The Principle of Linear Superposition

When two or more waves are present simultaneously at the same place, the resultant disturbance is the sum of the disturbances from the individual waves.

When 2 waves always meet condensation-to-condensation and rarefaction-to-rarefaction, they are said to be:

exactly in phase and to exhibit constructive interference

when 2 waves always meet condensation-to-rarefaction, they are said to be:

exactly out of phase and to exhibit destructive interference

Coherent

If the wave patters do not shift relative to one another as time passes

Diffraction

the bending of a wave around an obstacle or the edges of an opening

Two overlapping waves with slightly different frequencyes give rise to :

the phenomena of beats

Beat Frequency

The difference between the two sound frequencies