# Physics - Waves and Light

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1. WAVES
2. What is a wave?
transfer of momentum between two points
3. mechanical waves require what in order to travel?
medium
4. 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
5. sound in air is what kind of wave?
longitudinal
6. amplitude is always what sign?
positive
7. velocity of a wave is dictated by?
medium it's traveling in
8. what two aspects of the medium affect velocity of the wave?
• medium's resistance to change in:
• 1- shape (elasticity)
• 2- motion (inertia)
9. greater density medium makes wave travel faster or slower?
slower
10. heavier medium - faster or slower?
stiffer medium - faster or slower?
heaver slow waves down

stiffer mediums speed waves up
11. for a gas medium, velocity of the wave changes how with changing temperature?
velocity increases with temperature
12. do sound waves move more quickly through hot or cold gases?
hot
13. elastic and interial components of medium store....
elastic = potential energy

interial = stores kinetic energy
14. wave velocity is independent of...
frequency, wavelength, and amplitude
15. surface waves: transverse or longitudinal?
completely neither
16. intensity (what is it and units)
energy transfer per area

W/m2
17. intensity increases with the square of?
amplitude and frequency

greater (amplitude and frequency)2 = greater intensity
18. does intensity depend on medium?
yes

density and velocity
19. 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
20. intensity level measured in....
decibels (dB)
21. if intensity increases by a factor of 10, decibels increase by...

22. 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
23. constructive v. destructive
constructive = sum results in greater displacement

destructive = sum results in smaller displacement
24. superposition
any wave can be created by superposition of many sine waves
25. beat
occurs when two waves with slightly different frequencies are superimposed
26. how does beat work?
some points will be nearly in phase (constructive)

some points will be out of phase (destructive)
27. audible beats must have close frequencies?
yes,

in other words, the two frequencies shouldn't be too far aparat
28. first and second harmonic have a ratio of
1:2
29. beat frequency is equal to:
fbeat = I f1- f2 I
30. beat frequency is an alternating increase and decrease in....
intensity of the noise
31. pitch correlates to...
frequency

high frequency = high pitch
32. when a wave transfers from one medium to the next, does wavelength or frequency change?
frequency remains the same

wavelength changes
33. standing waves
node and antinodes
34. node
point of no displacement [in line]
35. antinode:
point that experiences maximum constructive interference
36. what is a harmonic series?
only certain wavelengths could create a standing wave
37. 1st harmonic: how many nodes and antinodes? length of rope?
fundamental wavelength

one antinode

length of rope = 1/2(wavelength)
38. second harmonic

two antinodes

L = 2/2 (wavelenth) = wavelength
39. each successive harmonic is create by
40. equation for length of rope
41. L = (n × wavelengthn)/2 (n = 1,2,3….)
42. equation for wavelenghtn
wavelength = wavelength/n
43. resonance
vibrate at is resonant frequency
44. how can you find resonant frequency?
velocity through a medium is constant,

• so when it resonates, its resonant frequency is
• v = (lambda)(freq.)
45. what does simple harmonic motion mean?
it repeats itself
46. what kind of function is it?
sinusoidal function of time
47. example of simple harmonic motion
standing in front of someone riding a bike: looks like they're peddling up and down

pendulum
48. equation for angular frequency
w = 2pif
49. in simple harmonic motion, how is acceleration related to distance?
directly proportional

but opposite signs
50. What relates acceleration and frequency?
square of the frequency
51. how does mass on pendulum affect motion?
it doesn't
52. period for pendulum (equation)
T = 2pi (L/g)1/2
53. when pendulum is in the middle (straight down) KE and PE are
KE is at its maximum

PE is at its minimum
54. what kind of curve is the KE of a pendulum?
sine curve

(simple harmonic motion)
55. 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
56. period (T) in simple harmonic motion
T = (2pi) x sq.rt.(m/k)

57. energy oscillates between...
KE and one or more forms of potential energy
58. LIGHT
59. What is an electromagnetic wave?
traveling oscillation of an electric and magnetic field
60. What kind of wave is what kind of wave?
transverse wave
61. How are electromagnetic fields generate?
acceleration of an electric charge
62. electromagnetic spectrum: energy and wavelength
inversely proportional:

E = hf = h(v/lambda)
63. 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
64. order of increasing energy
radio < microwaves < IR < ROYGBIV < UV rays < x rays < gamma rays
65. intensity of light is a measure of...
frequency of photons (photon energy stays the same)
66. what is monochromatic light?
light with a single frequency
67. index of refraction (equation)
n = c/v

• c = 3 x 108
• v = speed of light in medium
68. light waves travel faster or slower when propagating through a medium
slower

• index of refraction for air = 1
• other medium = greater than 1
what is the electromagnetic wave?
each photon = electromagnetic wave
70. dual nature of light - what do each reflect?
wave = propagation properties

particle = energy transformation
71. angle of refraction (equation)
n1sin1 = n2sin2
72. light's preferred path
shortest path possible
73. when light crosses into a new medium, what happens to frequency and wavelength?
frequency stays the same

wavelength changes
74. how does wavelength change, increase or decrease?
n2 is greater = wavelength decreases

n2 is less = wavelength increases

(inversely proportional)
75. energy of a photon
E = hf

h = 6.63 x 10-34
76. when light is refracted, while it still have the same amount of energy per photon?
yes,

just that some photons were reflected and others refracted
77. critical angle: what is it, and what is the equation?
all photons are reflected (none refracted)

sin-1(n2/n1)
78. What is dispersion of light?
different light frequencies travel at slightly different speeds

(index of refraction varies with frequency)
79. Do longer waves or shorter waves move faster?
longer waves - lower frequency
80. since longer waves move faster, is there a greater or lesser bending at the media interference?
less dramatic
81. What is diffraction?
when a wave moves through a small opening, it bends around the corners of it

bending = diffraction
82. 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
83. what happens when diffracted waves meet?
interference

forms bright and dark images
84. which produces bright and which dark images?
constructive = bright

destructive = dark
85. diffraction is part of light's wave or particle phenomenon?
wave
86. If light were purely a particle, what would happen when it moved through the slit?
no diffraction

all light would go directly to detector at the level of the slit.
87. mirrors and lenses: which reflect and which refract?
mirrors = reflect

lenses = refract
88. lenses: diverging and convergine (relative to mirror concave and convex)
diverging = concave

converging = convex

Thicker Center Converges
a sharper curve

straighter line = larger radius of curvature
90. what is the focal length?
focal point is separated from mirror/lens by the focal length (f)
91. focal length of mirror
92. focal length of lens - affected by:
• refractive index of lens (n1)
• substance around the lens (n2)
93. what is the magnification
ratio of size of image/object

"dido"
94. magnification (equation)
m = - (di/do) = (hi/ho)
95. what does negative in the magnification equation mean?
if both distance are positive, image is inverted
96. positive magnification means
negative magnification means
positive = upright image

negative = inverted image
97. thin lens equation:
1/f = (1/do) + (1/di)
98. System for Mirrors and Lenses
1. I (eye) am positive that real is inverted
99. 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
100. front and back for mirror and lens
eye is in front of mirror

behind lense
101. front and back - positive and negative
front = positive

behind = negative
102. What are negative, virtual and upright?
• convex mirrors
• diverging lenses
103. what are positive, real, and invert?
• concave mirrors
• converging lens
104. exception:
if object is within focal distance os concave mirror or converging lens: image is negative, virtual, upright
105. so, what is always negative
convex mirror, diverging lens
106. Power of lens (equation)
(1/f) = (1/di) + (1/do)
 Author: natalieplana ID: 82958 Card Set: Physics - Waves and Light Updated: 2011-05-01 15:12:07 Tags: NPMCAT Folders: Description: Waves, Light, and Optics Show Answers: