2.5 WAVE MOTION AND SOUND

What is a wave? A) A disturbance that transports energy without net particle movement B) A permanent movement of matter C) A stationary particle

A) A disturbance that transports energy without net particle movement

What do particles in a wave medium do? A) Travel permanently with the wave B) Vibrate about mean positions C) Remain completely still

B) Vibrate about mean positions

What is transferred by wave motion? A) A piece of the medium B) Mass only C) Energy

C) Energy

What is wavelength? A) Distance between identical locations in adjacent cycles B) Time for one cycle C) Maximum displacement

A) Distance between identical locations in adjacent cycles

What is period? A) Cycles per second B) Time for one complete vibrational cycle C) Energy per unit area

B) Time for one complete vibrational cycle

What is frequency? A) Distance between crests B) Maximum disturbance C) Number of complete waves passing a point per second

C) Number of complete waves passing a point per second

What is amplitude? A) Maximum disturbance from equilibrium B) Distance between waves C) Speed of energy transfer

A) Maximum disturbance from equilibrium

What is wave speed? A) Particle mass per second B) Rate at which energy is transported C) Amplitude per cycle

B) Rate at which energy is transported

Which behaviour can all waves exhibit? A) Only reflection B) Only absorption C) Reflection refraction diffraction and interference

C) Reflection refraction diffraction and interference

What is a mechanical wave? A) Energy transferred through a material medium B) Energy travelling only in vacuum C) A stationary pressure

A) Energy transferred through a material medium

How do mechanical particles transfer energy? A) One particle travels to the destination B) Each particle passes vibrational energy to the next C) Particles disappear

B) Each particle passes vibrational energy to the next

What are the two mechanical wave types? A) Circular and radial B) Static and thermal C) Transverse and longitudinal

C) Transverse and longitudinal

How do transverse particles vibrate? A) Perpendicular to energy transfer B) Parallel to energy transfer C) Without displacement

A) Perpendicular to energy transfer

What is a crest? A) Lowest point below equilibrium B) Highest point above equilibrium C) A compression

B) Highest point above equilibrium

What is a trough? A) Highest point above equilibrium B) A rarefaction C) Lowest point below equilibrium

C) Lowest point below equilibrium

Which is a transverse wave example? A) A wave on a string B) Sound in air C) A pressure pulse in gas

A) A wave on a string

What motion do floating objects show on water waves? A) Permanent forward motion B) Perpendicular up-and-down motion C) No motion

B) Perpendicular up-and-down motion

How do longitudinal particles vibrate? A) Perpendicular to energy transfer B) In a circular orbit C) Parallel to energy transfer

C) Parallel to energy transfer

What is a compression? A) Particles squashed close together B) Particles spaced far apart C) A crest

A) Particles squashed close together

What is a rarefaction? A) Particles compressed together B) Particles spaced apart C) A trough

B) Particles spaced apart

Which is a longitudinal-wave example? A) A guitar string wave B) A surface water crest C) Sound in air

C) Sound in air

Where can longitudinal mechanical waves travel? A) Solids liquids and gases B) Vacuum only C) Liquids only

A) Solids liquids and gases

What pressure corresponds to a compression? A) Lower pressure B) Higher pressure C) Zero pressure

B) Higher pressure

What pressure corresponds to a rarefaction? A) Higher pressure B) Maximum pressure C) Lower pressure

C) Lower pressure

Which seismic waves are longitudinal? A) Primary P-waves B) Secondary S-waves C) Surface waves only

A) Primary P-waves

What shape results when wave displacement is plotted against time? A) A square wave only B) A sinusoidal curve C) A straight horizontal line

B) A sinusoidal curve

What determines wave speed? A) Amplitude only B) Frequency only C) The nature of the medium

C) The nature of the medium

What remains constant for a given wave when energy changes? A) Frequency B) Amplitude C) Wavelength in every medium

A) Frequency

What does increased wave energy determine? A) Greater frequency necessarily B) Greater amplitude C) Zero period

B) Greater amplitude

Which equation gives wave speed? A) v = f/λ B) v = λ/f C) v = fλ

C) v = fλ

A wave has f=5 Hz and λ=2 m. What speed is it? A) 10 m/s B) 2.5 m/s C) 7 m/s

A) 10 m/s

Which equation gives frequency from speed and wavelength? A) f = vλ B) f = v/λ C) f = λ/v

B) f = v/λ

What angle represents one complete sinusoidal cycle? A) 90 degrees only B) 180 degrees only C) 360 degrees or 2π radians

C) 360 degrees or 2π radians

For t=0.6 s and T=2 s what phase angle in degrees is used? A) 108 degrees B) 60 degrees C) 360 degrees

A) 108 degrees

Which equation gives displacement using degrees? A) y = A cos(T/t) B) y = A sin(360t/T) C) y = t sin(A/T)

B) y = A sin(360t/T)

Which equation gives displacement using radians? A) y = A sin(T/2πt) B) y = 2πA/T C) y = A sin(2πt/T)

C) y = A sin(2πt/T)

What does y represent? A) Particle displacement from equilibrium B) Wave frequency C) Wavelength

A) Particle displacement from equilibrium

What is interference? A) Refraction at one surface B) Superposition when waves meet in space and time C) A change in mass

B) Superposition when waves meet in space and time

What happens when two waves pass through each other? A) They always stop B) They merge into matter C) They can emerge apparently unaffected

C) They can emerge apparently unaffected

What produces constructive interference? A) Coincident crests or troughs B) A crest and trough together C) Two unrelated frequencies only

A) Coincident crests or troughs

What is the result of constructive interference? A) Zero displacement B) Maximum amplitude C) No wave

B) Maximum amplitude

What produces destructive interference? A) Two crests coinciding B) Two troughs coinciding C) A crest coinciding with a trough

C) A crest coinciding with a trough

What is the result of destructive interference? A) Zero displacement at the coincidence B) Maximum amplitude C) A doubled frequency

A) Zero displacement at the coincidence

What must sources have for interference to be examined clearly? A) Different frequencies only B) Same frequency amplitude and phase difference C) Zero amplitude

B) Same frequency amplitude and phase difference

What does phase angle compare? A) Masses of two sources B) Wave speeds in vacuum C) Positions of particles on the same waveform

C) Positions of particles on the same waveform

When are two particles in phase? A) They occupy the same position at the same time B) They are 180 degrees apart C) They have different frequencies

A) They occupy the same position at the same time

What phase difference is in phase? A) An odd multiple of 180 degrees B) An integral multiple of 360 degrees C) 90 degrees only

B) An integral multiple of 360 degrees

What phase difference is out of phase? A) An integral multiple of 360 degrees B) Zero degrees C) An odd multiple of 180 degrees

C) An odd multiple of 180 degrees

What does coherent mean for two waves? A) Same frequency and constant phase difference B) Different amplitude and changing frequency C) No phase relation

A) Same frequency and constant phase difference

A wave starts a quarter wavelength after another. What phase difference is this? A) 45 degrees B) 90 degrees C) 180 degrees

B) 90 degrees

What produces a stationary wave? A) Two waves travelling together B) A single pulse C) Equal-frequency equal-amplitude waves travelling oppositely

C) Equal-frequency equal-amplitude waves travelling oppositely

What happens to peaks and troughs in a stationary pattern? A) They do not travel along the medium B) They move at wave speed C) They disappear

A) They do not travel along the medium

What is a node? A) A point of maximum displacement B) A fixed point of zero displacement C) A moving crest

B) A fixed point of zero displacement

What is an antinode? A) A point of zero displacement B) A compression only C) A fixed point of maximum displacement

C) A fixed point of maximum displacement

What is the spacing between adjacent nodes? A) Half a wavelength B) One wavelength C) A quarter wavelength

A) Half a wavelength

Where are antinodes located? A) At every node B) Midway between adjacent nodes C) Only at the source

B) Midway between adjacent nodes

Are nodes and antinodes necessarily points in a two-source pattern? A) They are always particles B) They are always travelling crests C) They can be fixed lines or areas

C) They can be fixed lines or areas

What gives an antinode in a ripple pattern? A) Coincident crests or troughs B) A crest and trough cancellation C) No superposition

A) Coincident crests or troughs

What gives a node in a ripple pattern? A) Two crests B) Crest and trough coincidence C) Two troughs

B) Crest and trough coincidence

What causes sound energy? A) Light photons only B) Static pressure with no motion C) Physical vibration of air particles

C) Physical vibration of air particles

What type of wave is sound in air? A) A longitudinal mechanical wave B) A transverse electromagnetic wave C) A stationary wave only

A) A longitudinal mechanical wave

What direction do sound particles vibrate? A) Perpendicular to propagation B) The same direction as propagation C) No direction

B) The same direction as propagation

What do sound particles do to transmit energy? A) Move permanently to the ear B) Reflect only from walls C) Collide with neighbouring particles

C) Collide with neighbouring particles

What does the eardrum convert? A) Sound energy into mechanical movement B) Heat into light C) Frequency into mass

A) Sound energy into mechanical movement

What unit measures sound intensity? A) Hertz only B) Decibel or dB C) Metres per second

B) Decibel or dB

What kind of scale is the decibel scale? A) Linear only B) A temperature scale C) Logarithmic

C) Logarithmic

What intensity reference is near-complete silence? A) 0 dB B) 10 dB C) 100 dB

A) 0 dB

A 10 dB increase represents what intensity change? A) A factor of 2 B) A factor of 10 C) A factor of 1000

B) A factor of 10

Which equation gives sound speed? A) v = f/λ B) v = λ/f C) v = fλ

C) v = fλ

What is the approximate speed of sound in air given? A) 330 m/s B) 33 m/s C) 3000 m/s

A) 330 m/s

Compared with air how fast does sound travel in water? A) About five times slower B) About five times faster C) At the same speed

B) About five times faster

Compared with air how fast does sound travel in steel? A) About twenty times slower B) At the same speed C) About twenty times faster

C) About twenty times faster

For a fixed medium if wavelength increases what happens to frequency? A) It decreases B) It increases C) It becomes zero

A) It decreases

Why does sound speed reduce with altitude in the notes? A) Pressure always increases B) Lower temperature and density reduce the speed C) Air becomes a solid

B) Lower temperature and density reduce the speed

Which temperature scale is used in the approximate sound-speed formula? A) Celsius only B) Fahrenheit only C) Kelvin

C) Kelvin

What does higher gas temperature do to local sound speed? A) It increases it B) It decreases it C) It has no effect

A) It increases it

What is wave intensity? A) Energy per unit wavelength B) Power per unit area C) Frequency per unit time

B) Power per unit area

Which equation gives intensity from power and area? A) I = PA B) I = A/P C) I = P/A

C) I = P/A

What is the area of a sphere of radius r? A) A = 4πr² B) A = 2πr C) A = πr

A) A = 4πr²

Which equation gives spherical-wave intensity? A) I = 4πPr² B) I = P/(4πr²) C) I = P/(4πr)

B) I = P/(4πr²)

How does intensity vary with distance? A) As r² B) Directly as r C) As 1/r²

C) As 1/r²

How does sound-pressure amplitude vary with distance in a spherical wave? A) As 1/r B) As 1/r² C) As r²

A) As 1/r

For a fixed source what happens to intensity at three times the distance? A) It becomes one third B) It becomes one ninth C) It becomes three times

B) It becomes one ninth

A 50 W source at 1 m has intensity about what value? A) 50 W/m² B) 0.398 W/m² C) 3.98 W/m²

C) 3.98 W/m²

A 50 W source at 3 m has intensity about what value? A) 0.44 W/m² B) 1.33 W/m² C) 3.98 W/m²

A) 0.44 W/m²

What unit measures sound frequency? A) Decibel B) Hertz C) Metre

B) Hertz

What frequency range is audible to humans in the notes? A) 0 to 100 Hz B) 20000 to 40000 Hz C) 20 to 20000 Hz

C) 20 to 20000 Hz

What determines pitch? A) Frequency B) Amplitude only C) Wavelength only

A) Frequency

What is infrasound? A) Frequency above 20000 Hz B) Frequency below 20 Hz C) Sound at 60 dB

B) Frequency below 20 Hz

What is ultrasound? A) Frequency below 20 Hz B) Any sound at 0 dB C) Frequency above 20000 Hz

C) Frequency above 20000 Hz

What is timbre or quality? A) The effect of the fundamental plus harmonics B) The loudness only C) The speed of sound only

A) The effect of the fundamental plus harmonics

What is the Doppler effect for sound? A) Sound speed becomes zero B) Observed frequency changes due to relative motion C) Amplitude becomes constant

B) Observed frequency changes due to relative motion

What happens to wavelength in front of a moving source? A) It is lengthened B) It is unchanged C) It is shortened

C) It is shortened

What happens to wavelength behind a moving source? A) It is lengthened B) It is shortened C) It becomes zero

A) It is lengthened

What frequency is observed when wavelength is shortened at fixed speed? A) Lower frequency B) Higher frequency C) No frequency

B) Higher frequency

Which quantity changes at the receiver in the notes? A) Transmitted frequency B) Wave speed in the medium C) Observed frequency

C) Observed frequency

What is red shift? A) Longer light wavelength from a receding source B) Shorter wavelength from an approaching source C) A sound intensity change

A) Longer light wavelength from a receding source

What can radar Doppler measurements estimate? A) Aircraft temperature only B) Aircraft velocity over the ground C) Sound intensity

B) Aircraft velocity over the ground

Which equation gives Doppler shift? A) fD = fR + fT B) fD = fT/fR C) fD = fR − fT

C) fD = fR − fT

If receiver frequency is 95 Hz and transmitter frequency is 100 Hz what is fD? A) −5 Hz B) 5 Hz C) 195 Hz

A) −5 Hz