Download Waves Review (Key)

Physics
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Date: _____________ Period: _______
Waves
(Unit Review)
Key Vocabulary
Absorption
Acoustical engineering
Acoustics
Additive color
Amplitude
Concave
Cones
Convex
Diffraction
Diffuse reflection
Doppler effect
Double Slit Experiment
Echo
Echolocation
Electromagnetic spectrum
Equilibrium
Fiber optics
Fluorescence
Frequency
Gamma rays
Harmonic absorber
Harmonic Motion
Hologram
Hyperopia
Incandescence
Incident ray
Index of refraction
Infrared Waves
Interference
Lasers
LED
Light intensity
Longitudinal Waves
Mach number
Microwaves
Mirage
Myopia
Natural frequency
Node
Normal
Opaque
Oscillation
Peak (Crest)
Period
Periodic force
Pitch
Prism
Radio waves
Real image
Reflection
Refraction
Resonance
Response
Restoring force
Rods
Snell’s Law
Sonar
Sonic Boom
Subtractive color
Surface Waves
Total internal reflection
Translucent
Transparent
Transverse Waves
Trough
Trichromatic color theory
Tuned Mass Dampener
Ultraviolet waves
Vibration
Virtual image
Visible light
Volume
Wavelength
X-rays
1. Compare and contrast linear motion with harmonic motion.
Harmonic motion is motion that is periodic or repeats. Linear motion on the other hand is movement in
one direction.
2. What distinguishes between a vibration and an oscillation?
The word oscillation means a motion that repeats regularly. The term vibration is another word used
for back and forth. People tend to use “vibration” for motion that repeats quickly and “oscillation” for
motion that repeats more slowly.
3. Give two examples of an earth oscillation.
Examples of earth oscillations include:
– Earth-Sun system (one year; orbit around sun)
– Earth-Moon system (28 days; moon around earth)
– Earth axis (24 hours; day and night)
– Earth’s wobble (22,000 years; 100s of miles for poles moving)
– Gyres in air and ocean currents (El Nino, etc.)
4. Explain what music is and how we hear it.
Music is sound produced by oscillators that we design with certain cycles that we enjoy hearing. We
hear it because the vibrations of the instrument create tiny oscillations in air pressure. The pressure
oscillations travel to your eardrum and cause it to vibrate. Vibrations of the eardrum move tiny bones
in the ear setting up more vibrations that are transmitted by nerves to the brain.
5. What is the relationship between period and frequency in a wave?
Frequency and period are inversely related.
𝑇=
1
𝑓
or 𝑓 =
1
𝑇
6. The spin rate of a CD-ROM varies according to the location on the disc from where data is being
accessed. When accessing data from the inner circles of the disc, the CD can spin at a rate as high as
400 revolutions per minute. Determine the frequency (in Hertz) and the period (in seconds) of the
spinning CD.
400 𝑟𝑒𝑣𝑜𝑙𝑢𝑡𝑖𝑜𝑛𝑠
1 𝑚𝑖𝑛𝑡𝑢𝑒
6.67 𝑟𝑒𝑣𝑜𝑙𝑢𝑡𝑖𝑜𝑛𝑠
𝑓=
𝑥
=
= 6.67 𝐻𝑧
𝑚𝑖𝑛𝑢𝑡𝑒
60 𝑠𝑒𝑐𝑜𝑛𝑑𝑠
𝑠𝑒𝑐𝑜𝑛𝑑
1
1
𝑇= =
= 0.15 𝑠𝑒𝑐𝑜𝑛𝑑𝑠 𝑝𝑒𝑟 𝑟𝑒𝑣𝑜𝑢𝑡𝑖𝑜𝑛
𝑓
6.67 𝐻𝑧
7. What is natural frequency and how does this relate to periodic force and resonance?
The natural frequency is the frequency (or period) at which a system naturally oscillates. Every
system that oscillates has a natural frequency. Since at the atomic level everything oscillates (or at least
vibrates) at some level, all materials have a natural frequency. As such all objects exhibit some
(however small it may be) internal periodic (repeated) force and if an external force matches that force
can produce resonance.
8. What is resonance and how does this impact the motion of an object? Give an example. Resonance
occurs when a periodic force has the same frequency as the natural frequency of the system. If the
force and the motion have the same frequency, each push adds resonance in three steps: the periodic
force, the system, and the response. The response is what the system does when you apply the periodic
force. In resonance, the response is very large compared to the strength of the force. Resonance occurs
when: (1) There is a system in harmonic motion, (2) There is a periodic force, and (3) The frequency of
the periodic force matches the natural frequency of the system. The Tacoma Narrow Bridge would be
an extreme example, but a playground swing where the child/occupant is pumping their legs helping to
keep the periodic motion going.
9. What is a tuned mass dampener? What is it used for?
A tuned mass dampener (also called a harmonic absorber) is a device mounted in structures to reduce
the amplitude of mechanical vibrations, especially those that create sway due to natural frequencies
with the intent of avoiding resonance. This allows the towers to sway small amounts without the large
movements that may cause motion sickness or the type of destruction seen with the Tacoma Narrows
bridge due to amplification.
10. What is a wave?
A wave is a traveling disturbance that carries energy from one place to another.
11. Draw a sine wave and label a crest, trough, amplitude, and wavelength.
amplitude
12. What is the difference between mechanical and electromagnetic waves?
Mechanical waves require a medium to travel though whereas electromagnetic waves do not.
13. Compare and contrast longitudinal and transverse waves.
For transverse waves the displacement of the medium is perpendicular to the direction of propagation of
the wave (electromagnetic). In longitudinal waves the displacement of the medium is parallel to the
propagation of the wave (mechanical; sound).
14. What is sound and how does it change with respect to amplitude and frequency?
Sound is produced when matter vibrates or moves back and forth very quickly. The sound wave
produced is a type of longitudinal wave. Amplitude is a measure of the amount of energy in a wave and
we hear it as volume. Frequency is a measure of the number of cycles per unit time. The more cycles
produced (faster vibrations), the higher the pitch of the sound. The fewer cycles (slower vibrations) the
lower the pitch of the sound.
15. Carina is rocking out to her favorite radio station - 102.3 FM. The station broadcasts radio signals with
a frequency of 1.023 x 108 Hz. The radio wave signal travel through the air at a speed of 2.997 x 108
m/s. Determine the wavelength of these radio waves.
𝑣 = 𝜆 ∗𝑓
2.997 ∙ 108 𝑚/𝑠 = 𝜆 ∗ 1.023 ∙ 108 𝐻𝑧
2.93 𝑚
16. What is the Doppler effect? How does this relate to the frequency of a sound wave?
If we remember the Big Bang Theory, the Doppler effect is the apparent change in the frequency of a
wave caused by relative motion between the source of the wave and the observer. As the object is
approaching, the wavelength gets compressed and the pitch increases (raises). As the object is moving
away, the wavelength gets elongated and the pitch decreases (lowers).
17. How does the Mach number relate to the speed of sound?
Mach number is the ratio of the speed of the object to the speed of sound.
𝑆𝑝𝑒𝑒𝑑 𝑜𝑓 𝑜𝑏𝑗𝑒𝑐𝑡
= 𝑀𝑎𝑐ℎ 𝑁𝑢𝑚𝑏𝑒𝑟
𝑆𝑝𝑒𝑒𝑑 𝑜𝑓 𝑆𝑜𝑢𝑛𝑑
18. At an airshow the Blue Angels were performing stunts and clocked at 1.18 Mach. This is what speed?
(HINT: Assume the speed of sound is 300 m/s)
𝑆𝑝𝑒𝑒𝑑 𝑜𝑓 𝑜𝑏𝑗𝑒𝑐𝑡
= 𝑀𝑎𝑐ℎ 𝑁𝑢𝑚𝑏𝑒𝑟
𝑆𝑝𝑒𝑒𝑑 𝑜𝑓 𝑆𝑜𝑢𝑛𝑑
𝑆𝑝𝑒𝑒𝑑 𝑜𝑓 𝑜𝑏𝑗𝑒𝑐𝑡
= 1.18 𝑀𝑎𝑐ℎ
300 𝑚/𝑠
𝑆𝑝𝑒𝑒𝑑 𝑜𝑓 𝑜𝑏𝑗𝑒𝑐𝑡 = 354 𝑚/𝑠
19. What is an echo? How is this used in echolocation and how does this relate to sonar?
An echo is a sound or series of sounds caused by the reflection of sound waves from a surface back to
the listener. The time delay is the distance divided by the speed of sound. It is possible to use this
information to calculate distance. This is how sonar and echolocation work. Sound bounces off the
object and back to the source of origin. The time it takes is dependent on the distance to the source.
20. How is most light produced?
Light is a form of energy and is mostly produced by atoms as they emit energy by rearrange electrons.
21. How does vision work? (HINT: provide a complete answer).
You see because light in the room reflects or emits from the object onto your eyes. If you were in a
perfectly dark room with no light, you would not be able to see. However, we see most of the world via
reflected light landing on the rods and cones at the back of the eye. According to the trichromatic
theory of color vision there are three receptors in the retina that are responsible for the perception of
color.
22. Compare and contrast incandescence with fluorescence.
Incandescence is the process of making light with heat from the thermal energy in atoms.
Fluorescence is the release of electrical energy as light from atoms.
23. What is the unit for light intensity? If one had 500 of this unit at one point, what would it have 4 times
as far away?
Light intensity uses the unit watts per square meter (W/m2). If we had 500 W/m2 of light intensity, if
we went 4 times as far away, we would end up with 1/42= 1/16.
500 𝑊/𝑚2
= 31.25 𝑊/𝑚2
16
24. Explain what each part of Einstein’s famous equation (E = mc2) represents and what this means.
The E = mc2 equation is part of Albert Einstein’s theory of special relativity that shows that the
increased relativistic mass (m) of a body comes from the energy of motion of the body—that is,
its kinetic energy (E)—divided by the speed of light squared (c2). This equation expresses the fact that
mass and energy are the same physical entity and can be changed into each other.
25. What are opaque, transparent, and translucent and how do they relate to light?
Opaque materials only absorb and reflect light – no light passes through them. Materials that allow
some light to pass through are known as translucent. Transparent materials transmit almost all the light
striking them, so you can see objects clearly through them.
26. From longest to shortest wavelength, list the colors of the rainbow found within white light.
Red, Orange, Yellow, Green, Blue, Indigo, Violet
27. Organize the following electromagnetic waves by wavelength from shortest to longest. Identify which
end has higher and lower energy.
gamma-rays, infrared, microwaves, radio, ultraviolet, visible light, and x-rays
Gamma, x-ray, ultraviolet, visible, infrared, microwaves, radio.
28. How do we use the various electromagnetic waves (listed above)? Give an example of each.
Radio waves are made by lightning or by astronomical objects. Artificially generated radio waves are
used for radio communication, broadcasting, radar and other navigation systems, communications
satellites, computer networks and innumerable other applications.
Microwave technology is extensively used for point-to-point telecommunications like your cell phone.
Microwaves are especially suitable for this use since they are more easily focused into narrower beams
than radio waves, allowing frequency reuse. Microwaves are used in spacecraft communication, and
much of the world's data, TV, and telephone communications are transmitted long distances by
microwaves between ground stations and communications satellites. Microwaves are also employed in
microwave ovens and in radar technology.
Most of the thermal radiation emitted by objects near room temperature is infrared. Infrared radiation
is used in industrial, scientific, and medical applications. Night-vision devices using active near-
infrared illumination allow people or animals to be observed without the observer being detected.
Infrared astronomy uses sensor-equipped telescopes to penetrate dusty regions of space, such as
molecular clouds; detect objects such as planets, and to view highly red-shifted objects from the early
days of the universe. Infrared thermal-imaging cameras are used to detect heat loss in insulated systems,
to observe changing blood flow in the skin, and to detect overheating of electrical apparatus. Other
applications include environmental monitoring, remote temperature sensing, short-ranged wireless
communication, spectroscopy, and weather forecasting.
Visible light refers to those frequencies of the electromagnetic spectrum that human eyes have evolved
to “see.”
Ultraviolet (UV) waves are used in tanning lamps and black light. While the majority of humans
cannot see ultraviolet radiation, it does cause many materials to fluoresce or glow, can cause chemical
reactions to occur, and can be seen by some birds and insects. UV is currently used in many medical
applications, in decontamination/ sterilization, in some optical sensors, and in forensic science.
Hard X-rays are widely used to image the inside of objects, e.g., in medical radiography and airport
security. X-rays are also used to help visualize and measure atom and molecules, a technique called xray crystallography.
Gamma rays are ionizing radiation, and are thus biologically hazardous (causing mutations or even
killing cells). However, gamma rays provide information about some of the most energetic phenomena
in the universe and are also used for diagnostic purposes in nuclear medicine in imaging techniques
(PET scan). They can also be used in processes of irradiation and while often cancer causing, in some
forms of cancer treatment.
29. Explain what color is and how we see it.
Color is the visual perception in humans to the spectrum of light (the different wavelengths of white
light; ROYGBIV) interacting in the eye with the spectral sensitivities of the light receptors (rods &
cones). The color an object appears depends on the colors of light it reflects. According to the
trichromatic theory of color vision there are three receptors in the retina that are responsible for the
perception of color. One receptor is sensitive to the color green, another to the color blue and a third to
the color red. These three colors can then be combined to form any visible color in the spectrum.
30. How does a color filter work?
A filter blocks all wavelengths except the one representing the color seen. So a blue filter absorbs all
wavelengths of light except that wavelength that we see as blue.
31. What is trichromatic color theory and how does this relate to color blindness?
The trichromatic theory of color vision states that there are three receptors in the retina that are
responsible for the perception of color. One receptor is sensitive to the color green, another to the color
blue and a third to the color red. These three colors can then be combined to form any visible color in
the spectrum. Individuals If one or more of your sets of cones did not function properly, you would not
be able to distinguish between certain colors. Most people who are said to be color-blind are not truly
blind to color, but they have difficulty distinguishing between a few colors, most commonly red and
green.
32. Compare and contrast additive and subtractive color. What are the primary colors for each?
The primary colors and mixing are different for light than they are for pigments. The primary colors for
light are:
a. Red
b. Green
c. Blue
The primary colors for pigment are:
d. Cyan
e. Magenta
f. Yellow
In additive color, adding more light moves toward white. In subtractive color, adding more pigments
takes wavelengths away and moves toward black.
33. When light interacts with matter, what four things can happen?
The light can:
a. Go through almost unchanged (transparency)
b. Go through but scattered (translucency)
c. Bounce off (reflection)
d. Transfer its energy to the material (absorption)
34. Compare and contrast reflection and refraction.
Reflection is the change in direction of a wave (bouncing back) at an interface between two different
media so that the wave returns into the medium from which it originated. Refraction is the change in
direction (bending) of a wave due to a change in its medium.
35. What is the law of reflection?
According to the law of reflection, light is reflected so that the angle of incidence always equals the
angle of reflection.
36. Compare a clear and diffuse reflection. What causes each?
Smooth, shiny surfaces have a clear reflection. Clear reflection is when light is uniformly redirected
off a surface. Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is
scattered in different directions.
37. What is the difference between a real and a virtual image?
A real image occurs where rays converge, whereas a virtual image occurs where rays only appear to
converge. Real images can be produced by concave mirrors and converging lenses if and only if the
object is placed further away from the mirror/lens than the focal point and this real image is inverted.
38. Draw a concave and a convex mirror. Explain what happens with each. Give an example of how we
use each.
Convex
Concave
A convex mirror is curved outward and enlarges the image. Examples include rear view mirrors
and store security mirrors. A concave mirror is curved inward and reduces the image. Examples
include telescopes, spotlights, and satellite dishes.
39. Complete the following ray diagrams for mirrors. List the characteristics for each image (HINT: SALT
– Size, Attitude (upright/inverted), Location, Type).
a.
b.
c.
d.
40. Draw a concave and a convex lens. Explain what each does to light rays.
See #38. Convex lenses converge (brings together) light rays. Forms real images and virtual images
depending on position of the object. Concave lenses diverge (send apart) light rays. All images are
erect and reduced.
41. Complete the following ray diagrams for lenses. List the characteristics for each image (HINT: SALT
– Size, Attitude (upright/inverted), Location, Type).
a.
b.
c.
42. Look at the picture below and answer the following questions.
The figure above shows a [concave / convex] lens and it [converges / diverges] light rays.
43. The index of refraction of diamond is 2.4. What is the speed of light in diamond if its speed in a
vacuum is 3.00 × 108m/s?
𝑐
𝑛=
𝑣
3.00 ∙ 108
2.4 =
𝑣
3.00 ∙ 108
𝑣=
= 1.25 ∙ 108
2.4
44. What is the index of refraction for an unknown material if the speed of light is 1.50 x 108 within the
material?
𝑐
𝑛=
𝑣
3.00 ∙ 108
𝑛=
1.50 ∙ 108
𝑛=2
45. A ray of light in air strikes a block of quartz at an angle of incidence of 30°. The angle of refraction is
20°. What is the index of refraction of the quartz?
𝑛𝑖 sin 𝜃𝑖 = 𝑛𝑟 sin 𝜃𝑟
(1.00028) sin 30° = 𝑛𝑟 sin 20°
𝑛𝑟 = 1.46
46. What is the angle of incidence for a light ray traveling from water into flint glass (n=1.70), if the angle
of refraction is 30°?
𝑛𝑖 sin 𝜃𝑖 = 𝑛𝑟 sin 𝜃𝑟
1.33 sin 𝜃𝑖 = 1.70 sin 30°
𝜃𝑖 = 39.7
47. Consider the optical fiber to the right. The
index of refraction of the inner core is 1.480,
and the index of refraction of the outer
cladding is 1.44. What is the critical angle for
the core-cladding interface? (HINT: Think
total internal reflection)
𝑛𝑖 sin 𝜃𝑖 = 𝑛𝑟 sin 𝜃𝑟
1.48 sin 𝜃𝑖 = 1.44 sin 90°
𝜃𝑖 = 76.6
48. The light beam shown in the figure makes an angle of 20.0° with
the normal line NN’ in the linseed oil. Determine the angles θ
and θ’. (The index of refraction of linseed oil is 1.48.)
𝑛𝑖 sin 𝜃𝑖 = 𝑛𝑟 sin 𝜃𝑟
1.00028 sin 𝜃𝑖 = 1.48 sin 20°
𝜃𝑖 = 30.4
𝑛𝑖 sin 𝜃𝑖 = 𝑛𝑟 sin 𝜃𝑟
1.48 sin 20° = 1.33 sin 𝜃𝑟
𝜃´𝑖 = 30.4
49. Explain what happens in a prism and how this relates to a rainbow.
When white light passes through a prism, the triangular prism refracts the light twice – once when it
enters the prism and again when it leaves the prism and reenters the air. Because the longer
wavelengths of light are refracted less than the shorter wavelengths are, red light is bent the least. As a
result of these different amounts of bending, the different colors are separated when they emerge from
the prism. Like prisms, rain droplets also refract light. When light enters near the side of a raindrop,
much of the light is internally reflected. This is how rainbows are formed. The refraction of the
different wavelengths can cause white light from the Sun to separate into the individual colors of visible
light. (HINT: Watch the video online if it is still unclear).
50. What are the four characteristics of a diamond that make it “brilliant.” Explain how this works in terms
of the physics of light. (HINT: 4Cs)
The brilliance of a diamond is based on the 4Cs (1) Carat, (2) Cut, (3) Color, and (4) Clarity. The
actual brilliance is the culmination of reflection, refraction, and scatter of light rays as they enter and
leave the diamonds surfaces. The more consistent the characteristics of the diamond the more the cut
will take advantage of the indices of reflection and refraction to produce sparkle.
51. Two converging lenses are shown in Figure C. Study the figure. Then answer the questions by writing
the correct letter. Which lens…
a) is more curved? __B__
f) Refracts light more? __B__
b) Is less curved? __A__
g) Has the shorter focal length? __B__
c) Is stronger? __B__
h) Has the longer focal length? __A__
d) Is weaker? __A__
i) Magnifies more? _____
e) Refracts light less? __A__
j) Magnifies less? _____
52. What does the double slit experiment teach us? Explain how the
experiment works.
The double slit experiment is strong evidence that light is a wave
because an interference pattern can only be created by the addition
of waves. The experiment creates a wave, which is split into two
separate waves that later combine into a single wave. Changes in
the path lengths of both waves result in a phase shift, creating an
interference pattern.
53. Compare and contrast constructive and destructive interference?
Constructive interference occurs when the crest of one wave overlaps the crest of another to combine
and produce a wave of increased amplitude, whereas destructive interference occurs when the crest of
one wave overlaps the trough of another and the two waves negate each other.
54. What is a spectroscope and how does it relate to diffraction?
When light with a mixture of wavelengths passes through a diffraction grating, each wavelength makes
a bright spot at a different place on the screen. As a result, the grating spreads the light out into its
separate wavelengths. That is why you see a rainbow when looking at a bright white light trough a
diffraction grating. A spectrometer is a device that use a diffraction grating to create a spectrum. The
spectrometer has a printed scale that allows you to read different wavelengths of light directly from the
pattern of light made by the grating.
55. Label the central spot in the diffraction pattern below as well as the 1st order, 2nd order, etc.
central spot
first order
second order
56. What is polarization? Compare vertical versus horizontal polarization.
Polarization is the direction of the oscillation of the wave perpendicular to the direction the wave
moves. Only transverse waves can have polarization. An easy way to think about polarization is to
think about shaking a spring back and forth. Waves move along the spring in its long direction. The
oscillation of the transverse wave is perpendicular to the direction the wave travels. If the spring is
shaken up and down it makes vertical polarization. If the spring is shaken back and forth it makes
horizontal polarization.
57. What is a laser? It is identified as monochromatic, coherent, and collimated. What does this mean?
A laser is a device that generates an intense beam of coherent monochromatic light (or other
electromagnetic radiation) by stimulated emission of photons from excited atoms or molecules. The
term laser originated as an acronym for Light Amplification by Stimulated Emission of Radiation.
This means that the light from a laser contains exactly one color or wavelength rather than a lot of
different wavelengths (monochromatic). It also means that all the wavelengths are in phase. All the
wave crests (high points) and troughs (low points) are lined up (coherent). Lastly, it means, while light
waves from ordinary sources (such as flashlights, lightbulbs, or the Sun) spread out in all directions
laser light waves all travel in the same direction, exactly parallel to one another. This means that laser
light beams are very narrow and can be concentrated on one tiny spot (collimated).
58. What is a hologram? How does it work?
Holograms are two-dimensional surfaces that show absolutely precise, three-dimensional images of real
objects. If you look at these holograms from different angles, you see objects from different
perspectives, just like you would if you were looking at a real object. Some holograms even appear to
move as you walk past them and look at them from different angles. A hologram is created by a
photographic technique that records the light scattered from an object, and then presents it in a way that
appears three-dimensional. Large-scale holograms, illuminated with lasers or displayed in a darkened
room with carefully directed lighting create the appearance of 3D viewing.
59. What is fiber optics and how does it work?
Fiber optics is the use of thin flexible fibers of transparent solids to transmit light signals. The light in a
fiber-optic cable travels through the core by constantly bouncing from the cladding (total internal
reflection). Because the cladding does not absorb any light from the core, the light wave can travel
great distances.
60. What is a mirage and how does it work?
A mirage is an optical illusion caused by atmospheric conditions, especially the appearance of a sheet
of water in a desert or on a hot road caused by the refraction of light from the sky by heated air.