Snell's law for
- We have used a Newton's particle model and Huygens' wave model
to describe the propagation of light rays. Both of these models correctly
predict Snell's law for the refraction (bending) of light as it moves from
one homogeneous medium into another where the speed of light differs from the
speed in the first medium. Discuss how they do so and what each model has to
assume about the speed of light in a more dense medium in order to describe
- We typically deal with
sound that has wavelengths comparable to the objects it interacts with (on
the order of a few centimeters to a few meters) so we don't usually talk
about "sound rays" or Snell's law for sound. But
if we are working with high frequency ultrasound, as is used currently in
many medical probes, it would be appropriate to consider it. We are pretty
certain of a couple of relevant facts about sound:
- Sound propagates as a wave.
- The speed of sound is greater in a dense medium.
Discuss what this would means for Snell's law for sound. Do you expect a ray of sound coming onto a denser medium to bend towards the normal (like light) or away from the normal? Explain your reasoning.
- Can we have the analog of total internal reflection for sound? If so, this
could have severe implications for imaging using ultrasound. The speed of
sound for some relevant media are given below. Determine which boundaries
between two media could lead to total reflection of sound rays. Describe the
configuration (entering from which medium) and find the angle above which
total reflection occurs.*
||Speed of Sound
* Data taken from J. R. Cameron and J. G. Skofronick, Medical Physics (John
Wiley & Sons, Inc., 1978) p. 255.
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April 29, 2006: OP30