Chp' 29: Reflection and Refraction

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Chp. 29 Reflection and Refraction
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1. What happens when a wave is reflected?

• A wave is reflected when it bounces off the
  boundary between two media. All or part of the
  wave can be reflected. All types of waves can be
  reflected (sound, light, etc.).

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2. Why do metals such as aluminum and silver make
good mirrors?

• Metals such as silver and aluminum make good
  mirrors because like most metals they are rigid
  to light waves. Their natural frequency does not
  match the frequencies of visible light and they
  will not resonate and absorb the light. Instead
  the light is reflected.
• These metals can also be polished so that their
  surfaces are very smooth which allows the to
  reflect light better.

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3. Describe the Law of Reflection by drawing a
diagram that labels the incidence ray, reflected
ray, normal, reflecting surface, angle of
incidence, and angle of reflection.

• See Figure 29.3, page 444. The Law of Reflection
  states that Angle of incidence Angle of
  reflection. The law applies to partially
  reflected and totally reflected waves.

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A angle of incidence
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4. What is a virtual image and explain how the
virtual image changes with the three types of
mirrors. You may draw diagrams for your
explanation.

• See Figure 29.6 and 29.5, page 445. A virtual
  image is an image that appears behind the surface
  of a mirror. It is not physically real. If a
  mirror is flat, the virtual image is the same
  size and distance as the actual object. If the
  mirror is convex, the virtual image is smaller
  and appears to be closer than the actual object.
  If the mirror is concave, the virtual image
  appears larger and farther away than the actual
  object.

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5. What is the difference between a diffuse
reflector and a polished reflector?

• A diffuse reflector has an uneven or rough
  surface that causes waves to scatter (leave at
  different angles) when they reflect. A polished
  a reflector has a smooth surface that allows the
  waves to reflect at the same angles.

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6. What determines whether a reflector is
polished or diffuse?

• Polished reflectors have differences in surface
  elevations that are less than 1/8 of a
  wavelength. Diffuse reflectors have differences
  in surface elevations greater than 1/8 of a
  wavelength.

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7. What is acoustics and why is it important?

• Acoustics is the study of sound properties. It
  is important to the designers of buildings,
  freeways, and airports, for example, in order to
  get a good balance between unwanted noise
  (pollution) and desired sound.

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8. How are concert halls designed to control
reverberation and absorption? You may use
diagrams in your answer.

• Concert walls and ceilings are designed to direct
  the sound to all points in the hall evenly.
  Special material is used to cover parts of the
  walls and ceilings that control the amount of
  sound absorption. This prevents too many sound
  waves bouncing (through echoes) around the
  concert hall at one time. Too many sound waves
  overlapping each other at the same time can cause
  the sound to be come garbled through
  interference. This type of sound wave
  interference is called reverberation.

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9. What is refraction?

• Refraction is the bending of a wave when it
  travels from one medium to another.

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10. What factors cause sound to be refracted?

• Sound wave refraction can be caused by
  differences in air temperature and air pressure.

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11. What factors cause light to be refracted?
Draw a diagram to explain your answer.

• Light is refracted as it changes as it passes
  from one medium to another or through areas of
  different temperature or density.

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12. Explain the phenomena of a mirage?

• A mirage is caused by differences in air
  temperature. Air close to the ground is hotter
  than air farther from the ground. Differences in
  temperature cause differences in density, so
  light rays refract as they travel through the
  different temperatures of air. The refraction
  creates a virtual image (not real). The virtual
  image can be seen only at a certain distance from
  the actual object. This is why the virtual
  object disappears as you try to approach it.

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13. What is dispersion and how is it responsible
for separating the colors of white light in a
prism?

• Dispersion is the separation of light into colors
  according to their frequencies. Because each
  color of light has a different frequency, it also
  has a different wavelength. The difference in
  wavelength causes different colors of light to
  bend or refract at different angles as they go
  from one medium to another. Because of the shape
  of a prism, light is refracted twice, once
  entering the prism and once leaving. Because the
  light is refracted twice, the total difference in
  refraction is enough to totally separate white
  light into the color spectrum.

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14. How is dispersion responsible for rainbows?

• Sunlight, which is white light, is dispersed into
  a color spectrum when it is double refracted in
  water drops in the sky. The sunlight has to
  enter the drops at a certain angle and observers
  must be at a certain distance on the ground in
  order to see the color spectrum, or rainbow, that
  is produced.

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15. What is the critical angle and how is it
related to internal reflection?

• The critical angle is the angle at a light wave
  can no longer pass through the boundary from one
  medium to another. The wave becomes internally
  reflected back into the original medium. When a
  light wave passes the critical angle, it is
  totally internally reflected.

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16. Explain how fiber optics work and how they
are useful.

• In fiber optics, light is internally reflected or
  piped through a length of optical or transparent
  wire or tubing. Fiber optics is useful in
  medicine, engineering, and communications because
  information can be transmitted at the speed of
  light.