00:01
So in the first part of this problem, we'll look at the doppler effect, which looks at an object that is radiating sound waves.
00:10
Now, usually, if the object is stationary, the waves are moving at some velocity, say, c for the speed of light, or usually for sound, we consider, but works the same for light waves.
00:23
At a certain frequency of sound, we get the waves as a certain spacing.
00:27
But as the object moves, you can imagine that the wave itself still travels at speed c, still traveling at a certain speed c, but the object is traveling with it and kind of chasing the sound waves.
00:45
If in the limit where, say, the object's moving at the speed of light, speed of sound, the sound wave travels with it and they all just...
00:54
If the object's traveling at c, then all the waves traveling at c just stack up in front of it, right, as a sonic wave right at mach 1.
01:04
But if the object is moving in the direction of the sound waves, then the waves stack up because they are...
01:13
The speed that they travel relative to the object is less because they travel at a speed relative to the earth, right, the wave speed.
01:26
So when we're looking at the observer and the emitter travels towards them, the waves are compressed.
01:46
And when we compress the waves in time, we see more of them, so the frequency increases.
01:52
In the next part for electrical current, it is electrons that flow...