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Part A Refraction
When a wavefront changes direction due to entering a new medium, we say the wavefront has been refracted. However, refraction occurs whenever a wave passes from one medium to another; thus in certain conditions, refraction can occur even if there is no change in wavefront direction.
Part B Wave velocity, wave frequency, and wavelength
The velocity of a mechanical or electromagnetic wave depends on the medium.
The frequency does not change when a wave is refracted.
Because the wave must be continuous across the boundary, the frequency does not change when waves are refracted. If the frequency remains constant and the velocity changes, then the wavelength must also change because:
If the frequency is constant, the velocity will be proportional to the wavelength. This means that if the wave velocity is lower in the second medium, the wavelength in the second medium will be shorter than in the first medium. If the wave travels more quickly in the second medium, then the wavelength will be longer in the second medium.
Therefore, during refraction:
The velocity of the wave changes and
The frequency of the wave stays constant so
The wavelength of the wave must change.
Part C Wavefront parallel to boundary between media
If the wave travels from the slower medium into the faster medium, the refraction is reversed.
Part D Wavefront parallel to boundary between media
We can understand why a wavefront changes direction by referring to figure 2.4.2 (1).
First, let’s note that the wavefront has to remain continuous; it can’t be split in two.
Assume the wave was initially traveling with a velocity in the first medium and, after entering the second medium, decreases its velocity to When point C enters the new medium, it will travel more slowly than point A. Point C has to travel to point D position at the same time t as point A has to travel to point B position.
The right-hand side of the wavefront ‘catches up with the left hand during this time and changes the direction of the wave’s velocity in the new medium.
0:00 Introduction
0:03 2.4.2.1 Waves Entering Different Media
1:17 Properties of a Refracted Wave
2:18 Changes in a Refracted Wave
3:05 Changing Direction
4:18 Refraction and the Normal
5:53 Refraction of Light
6:44 Perceiving Refraction
