The speed of light in different materials

You can ride a bicycle fast on hard pavement, but when you switch surfaces to sand, gravel, or mud you must slow down. Your speed on a bicycle depends on the medium you are traveling on. In the same way, the observed speed of light depends on the properties of the medium in which the light travels. Read the text aloud Show What does speed have to do with refraction?
Analogy between vehicle tires traveling from pavement to mud and light traveling from air to glass
The physical phenomenon of refraction—where light bends as it propagates from one medium to another—is a consequence of the change in the speed of light between those two media. The index of refraction for a medium, such as glass or water, represents how the speed of light has changed relative to a vacuum and is described by equation (22.2). Read the text aloud
(22.2) n= c v
n  = index of refraction
c  = speed of light in a vacuum (m/s)
v  = speed of light in medium (m/s)
Index of refraction
When the speed of light v changes as it moves from one medium to another, how are the frequency f and/or wavelength λ affected? Frequency cannot change because the number of waves per second that arrive must also depart. Instead, the wavelength changes from one medium to another (c = ). Look at the illustration above. Notice how the spacing between waves is smaller in glass than in air. The wavelength of light is shorter in glass than in air because the speed of light is lower in glass than in air. Read the text aloud Show Energy of light does not change upon refraction
What is the speed of light through saltwater if its index of refraction is 1.34?
Asked: speed of light v in saltwater
Given: index of refraction of saltwater, nw = 1.34;
speed of light in air (nearly same as a vacuum), c = 3.0×108 m/s
Relationships: index of refraction for water, nw = c/v
Solution: Solve for the speed of light in water by multiplying by v: v× n w = v ×(c/ v ) then dividing by nw: (v n w )/ n w =c/ n w v=c/ n w v=(3.0× 10 8  m/s)/1.34=2.2× 10 8  m/s
Answer: v = 2.2 × 108 m/s
Read the text aloud
When traveling through diamond, light travels at approximately 1.25 × 108 m/s. What is diamond’s index of refraction?
  1. 0.42
  2. 1
  3. 1.75
  4. 2.4
  5. Show
What is the index of refraction for a vacuum?
  1. 0
  2. 1
  3. 3×108
  4. 3.14159
Estimate the value for the index of refraction for air (na).
  1. na < 0
  2. 0 < na < 1
  3. 1 < na < 1.33
  4. 1.33 < na
Why are none of the indices of refraction less than 1? Show

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