Lect 6: Waves Flashcards
the transfer of momentum and energy from one point to another
3 types: mechanical, electromagnetic, and matter
wave
type of wave that obeys laws of physics
need to travel through a medium
mechanical wave
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
2 types of mechanical waves
transverse
longitudinal
type of mechanical wave where the medium is displaced perpendicularly to the wave
i.e. waves on a string
transverse wave
type of mechanical wave where the medium is displaced parallel to the wave
i.e. sound waves
longitudinal wave
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)
the number of wavelengths that pass a fixed point in one second
(cycles / second)
SI Unit = Hertz or 1 / sec
frequency (f)
Equation: Wave velocity
*Dictated by MEDIUM
V(wave) = frequency * wavelength
Note: MEDIUM dictates wave velocity, not the frequency or the wavelength
reciprocal of frequency
number of seconds it takes for one wavelength to pass a certain point
(seconds / cycle)
period (T)
Equation: Period
Period (T) = 1 / f
a wave’s maximum displacement from 0
always positive
Amplitude (A)
A wave function is always plotted against either ______ or _____
displacement or time
A medium’s _____ and _____ affect the velocity of a wave
elasticity (∆ shape)
inertia (∆ motion)
an object’s tendency to resist motion
inversely proportional to velocity
Intertia
For a gas, velocity ______ with temperate
increases
Waves (speed up / slow down) through a heavy medium
slow down
Waves (speed up / slow down) through a stiff medium
speed up
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)
The wave source determine’s a wave’s _____ and ______.
Amplitude & Frequency
The medium through which a wave travels determines _____ and ______
Density and velocity
artificial scale to describe intensities
SI unit = Decibel (dB)
Intensity level (b)
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
