Physics - Waves and Light
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What is a wave?
transfer of momentum between two points
mechanical waves require what in order to travel?
transverse v. longitudinal wave
transverse: medium is displaced perpendicularly to direction of wave propagation
longitudinal: medium is displaced parallel to the direction of wave propagation
sound in air is what kind of wave?
amplitude is always what sign?
velocity of a wave is dictated by?
medium it's traveling in
what two aspects of the medium affect velocity of the wave?
- medium's resistance to change in:
- 1- shape (elasticity)
- 2- motion (inertia)
greater density medium makes wave travel faster or slower?
heavier medium - faster or slower?
stiffer medium - faster or slower?
heaver slow waves down
stiffer mediums speed waves up
for a gas medium, velocity of the wave changes how with changing temperature?
velocity increases with temperature
do sound waves move more quickly through hot or cold gases?
elastic and interial components of medium store....
elastic = potential energy
interial = stores kinetic energy
wave velocity is independent of...
frequency, wavelength, and amplitude
surface waves: transverse or longitudinal?
intensity (what is it and units)
energy transfer per area
intensity increases with the square of?
amplitude and frequency
greater (amplitude and frequency)2 = greater intensity
does intensity depend on medium?
density and velocity
increase area = decrease intensity: snapping fingers example
propagates waves in all directions
energy is constant, but area is over a larger sphere
decrease in intensity of the sound
intensity level measured in....
if intensity increases by a factor of 10, decibels increase by...
addition of 10 decibels
adding 2 zeros to intensity = adding 20 decibels
in phase v out of phase
in phase: same wavelength, start at same point
out of phase: travel different distances but arrive at same point
constructive v. destructive
constructive = sum results in greater displacement
destructive = sum results in smaller displacement
any wave can be created by superposition of many sine waves
occurs when two waves with slightly different frequencies are superimposed
how does beat work?
some points will be nearly in phase (constructive)
some points will be out of phase (destructive)
audible beats must have close frequencies?
in other words, the two frequencies shouldn't be too far aparat
first and second harmonic have a ratio of
beat frequency is equal to:
fbeat = I f1- f2 I
beat frequency is an alternating increase and decrease in....
intensity of the noise
pitch correlates to...
high frequency = high pitch
when a wave transfers from one medium to the next, does wavelength or frequency change?
frequency remains the same
node and antinodes
point of no displacement [in line]
point that experiences maximum constructive interference
what is a harmonic series?
only certain wavelengths could create a standing wave
1st harmonic: how many nodes and antinodes? length of rope?
length of rope = 1/2(wavelength)
created by adding another node
L = 2/2 (wavelenth) = wavelength
each successive harmonic is create by
adding another node
equation for length of rope
L = (n × wavelengthn)/2 (n = 1,2,3….)
equation for wavelenghtn
wavelength = wavelength/n
vibrate at is resonant frequency
how can you find resonant frequency?
velocity through a medium is constant,
- so when it resonates, its resonant frequency is
- v = (lambda)(freq.)
what does simple harmonic motion mean?
it repeats itself
what kind of function is it?
sinusoidal function of time
example of simple harmonic motion
standing in front of someone riding a bike: looks like they're peddling up and down
equation for angular frequency
w = 2pif
in simple harmonic motion, how is acceleration related to distance?
but opposite signs
What relates acceleration and frequency?
square of the frequency
how does mass on pendulum affect motion?
period for pendulum (equation)
T = 2pi (L/g)1/2
when pendulum is in the middle (straight down) KE and PE are
KE is at its maximum
PE is at its minimum
what kind of curve is the KE of a pendulum?
(simple harmonic motion)
Hooke's law: mass hanging from a spring:
forces are greatest when? acceleration is constant?
forces are greatest when spring is fully compressed or fully extended
since F = ma, and a is also greatest
[Hooke's law: F=-k x change in x
period (T) in simple harmonic motion
T = (2pi) x sq.rt.(m/k)
energy oscillates between...
KE and one or more forms of potential energy
What is an electromagnetic wave?
traveling oscillation of an electric and magnetic field
What kind of wave is what kind of wave?
How are electromagnetic fields generate?
acceleration of an electric charge
electromagnetic spectrum: energy and wavelength
E = hf = h(v/lambda)
electromagnetic spectrum (left to right) inc. or dec. wavelength and frequency
left to right - dec. wavelength, inc. frequency
so moving left to right = increasing energy
order of increasing energy
radio < microwaves < IR < ROYGBIV < UV rays < x rays < gamma rays
intensity of light is a measure of...
frequency of photons (photon energy stays the same)
what is monochromatic light?
light with a single frequency
index of refraction (equation)
n = c/v
- c = 3 x 108v = speed of light in medium
light waves travel faster or slower when propagating through a medium
- index of refraction for air = 1
- other medium = greater than 1
light made of photons:
what is the electromagnetic wave?
each photon = electromagnetic wave
dual nature of light - what do each reflect?
wave = propagation properties
particle = energy transformation
angle of refraction (equation)
n1sin1 = n2sin2
light's preferred path
shortest path possible
when light crosses into a new medium, what happens to frequency and wavelength?
frequency stays the same
how does wavelength change, increase or decrease?
n2 is greater = wavelength decreases
n2 is less = wavelength increases
energy of a photon
E = hf
h = 6.63 x 10-34
when light is refracted, while it still have the same amount of energy per photon?
just that some photons were reflected and others refracted
critical angle: what is it, and what is the equation?
all photons are reflected (none refracted)
What is dispersion of light?
different light frequencies travel at slightly different speeds
(index of refraction varies with frequency)
Do longer waves or shorter waves move faster?
longer waves - lower frequency
since longer waves move faster, is there a greater or lesser bending at the media interference?
What is diffraction?
when a wave moves through a small opening, it bends around the corners of it
bending = diffraction
size of opening, relative to wavelength of the wave - and how will that affect bending of the wave
the smaller the hole, the greater the spreading of light
so, small opening = long wavelength = more bending
what happens when diffracted waves meet?
forms bright and dark images
which produces bright and which dark images?
constructive = bright
destructive = dark
diffraction is part of light's wave or particle phenomenon?
If light were purely a particle, what would happen when it moved through the slit?
all light would go directly to detector at the level of the slit.
mirrors and lenses: which reflect and which refract?
mirrors = reflect
lenses = refract
lenses: diverging and convergine (relative to mirror concave and convex)
diverging = concave
converging = convex
Thicker Center Converges
radius of curvature:
decrease radius of curvature is...
a sharper curve
straighter line = larger radius of curvature
what is the focal length?
focal point is separated from mirror/lens by the focal length (f)
focal length of mirror
focal length of lens - affected by:
- refractive index of lens (n1)
- substance around the lens (n2)
- radii of curvature
what is the magnification
ratio of size of image/object
m = - (di/do) = (hi/ho)
what does negative in the magnification equation mean?
if both distance are positive, image is inverted
positive magnification means
negative magnification means
positive = upright image
negative = inverted image
thin lens equation:
1/f = (1/do) + (1/di)
System for Mirrors and Lenses
1. I (eye) am positive that real is inverted
images on side of "eye" are always....
images on the other side are always...
side of eye = positive, real, and inverted
other side = negative, virtual, and upright
front and back for mirror and lens
eye is in front of mirror
front and back - positive and negative
front = positive
behind = negative
What are negative, virtual and upright?
- convex mirrors
- diverging lenses
what are positive, real, and invert?
- concave mirrors
- converging lens
if object is within focal distance os concave mirror or converging lens: image is negative, virtual, upright
so, what is always negative
convex mirror, diverging lens
Power of lens (equation)
(1/f) = (1/di) + (1/do)
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