Lect 6: Waves Flashcards by Taylor Walker

the transfer of momentum and energy from one point to another
3 types: mechanical, electromagnetic, and matter

wave

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type of wave that obeys laws of physics

need to travel through a medium

mechanical wave

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type of medium that is perfectly elastic; wave maintains its shape; does not disperse
i.e. Ideal waves
ALL materials on the MCAT

nondispersive medium

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2 types of mechanical waves

transverse

longitudinal

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type of mechanical wave where the medium is displaced perpendicularly to the wave
i.e. waves on a string

transverse wave

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type of mechanical wave where the medium is displaced parallel to the wave
i.e. sound waves

longitudinal wave

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measured from any point on a wave to the point where the wave repeats itself (i.e. peak to peak / trough to trough)
x-axis = displacement of the wave
SI unit = meters

wavelength (lambda)

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the number of wavelengths that pass a fixed point in one second
(cycles / second)
SI Unit = Hertz or 1 / sec

frequency (f)

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Equation: Wave velocity

*Dictated by MEDIUM

V(wave) = frequency * wavelength

Note: MEDIUM dictates wave velocity, not the frequency or the wavelength

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reciprocal of frequency
number of seconds it takes for one wavelength to pass a certain point
(seconds / cycle)

period (T)

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Equation: Period

Period (T) = 1 / f

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a wave’s maximum displacement from 0

always positive

Amplitude (A)

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A wave function is always plotted against either ______ or _____

displacement or time

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A medium’s _____ and _____ affect the velocity of a wave

elasticity (∆ shape)

inertia (∆ motion)

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an object’s tendency to resist motion

inversely proportional to velocity

Intertia

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For a gas, velocity ______ with temperate

increases

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Waves (speed up / slow down) through a heavy medium

slow down

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Waves (speed up / slow down) through a stiff medium

speed up

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defines Power (rate at which a wave transfers Energy)
increases w/ the SQUARE of the AMPLITUDE and SQUARE of the FREQUENCY
SI unit = W / m^2

Intensity (I)

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The wave source determine’s a wave’s _____ and ______.

Amplitude & Frequency

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The medium through which a wave travels determines _____ and ______

Density and velocity

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artificial scale to describe intensities

SI unit = Decibel (dB)

Intensity level (b)

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If Intensity increases by a factor of 10, the decibels increase by ______

10 decibels

If Intensity increases by a factor of 100, the decibels increase by ______

20 decibels

If I add 1 zero to intensity, I add _____ decibels

10 decibels

relates wavelength, frequency, place, and time or origin represented by a horizontal shift on a graph each wave represents 360º

phase of a wave

two waves of the same WAVELENGTH that begin at the same point

"in phase"

waves that are transverse and occupy the same space | add displacements at each point along the wave to form a new wave

Interference

the sume of the displacements of two waves creates a larger displacement

constructive interference

the sum of the displacements of two waves results in a smaller net displacement

destructive interference

occurs when 2 waves with slightly different FREQUENCIES are superimposed will experience BOTH constructive and destructive interference at different points

beat

difference in the frequency of the original two waves must = 0 for an instrument in perfect tune alternates up and down in intensity of the noise

beat frequency

Equation: Beat frequency:

f (beat) = | f1 - f2 |

what a tuner hears frequency creating this = the average of the frequencies from the fork and the instrument proportional to frequency

Pitch

the orientation of this waves depends on the density of the two media denser media: INVERTS wave less dense medium: wave is turned UP

reflected up

When a wave transfers from 1 medium to another, ____ changes but _____ stays the same

wavelength changes | frequency stays the same

the point where two sine waves w/ the same wavelength traveling in opposite directions collide on a perfectly elastic string does NOT move (x = 0)

node

points on perfectly elastic string where 2 sine waves w/ equal wavelengths experience the maximum constructive interference

antinode

a perfectly elastic string holds still at the nodes and moves violently up and down at the antinodes in this type of wave

standing wave

list of wavelengths from LARGEST to SMALLEST of possible standing waves

Harmonics

longest wavelength in a harmonic; created w/ the fewest nodes (2) distance from one medium to another = 1/2 * wavelength

Fundamental wavelength / first harmonic

created by adding another node between the two media in a harmonic distance between the two media = wavelength

second harmonic / wavelength 2

If only one side of a string is tied down or only one end of a pipe is open, the untied or open end is an ______. *When this happens, all of the even numbered harmonics are missing, and the length of the pipe/string equals the number of harmonics times the wavelength divided by 4

antinode

If both sides of a string are tied down or both sides of a pipe are open, both sides of the pipe / string are called _____. *In this case, the length of the pipe/string equals the number of nodes times the wavelength divided by 2

nodes

causes by a standing wave | to vibrate at a string's natural frequency

resonate

a wave's natural frequency | found for any given harmonic by v = frequency * wavelength

resonant frequency

condition where the natural frequency and the driving frequency are equal for a wave

resonance

any motion that repeats itself

harmonic motion (periodic motion)

a perfect sine wave specific type of harmonic motion sinusoidal function in time objects in this type of motion exhibit similar properties: -acceleration is directly proportional to the displacement but w/ the OPPOSITE sign -aceleration and displacement are related by the square of the frequency -No energy is lost to the surroundings in the oscillation b/w kinetic energy and potential energy Ex: Pendulum Ex: Mass bouncing on the end of a massless spring

simple harmonic motion

simple harmonic motion that switches between kinetic and potential energy no energy lost to surroundings Ex: Pendulum

oscillation

Waves are unaffected by speed of the source if the sources moves relative to the receiver, each wave travels a different distance and receiver gets them at different frequencies

Doppler Effect

When teh source and observer get closer to each other (move toward each other) observed frequency ______ and observed wavelength ____

observed frequency increases | wavelength decreases

Equations: Doppler Effect

∆f / f (s) = v / c ∆v / wavelength (s) = v / c Note: v = speed at which objects approach each other

If the light source and the observer approach each other, _____ shortens and shows a blue shift.

Wavelength

If the light source and the observer move away from each other, wavelength lengthens and shows a ______ shift.

Red

Objects moving in the same direction at the same speed have no _____ and relative velocity = 0, so ∆f = 0

Doppler Effect