IB Physics C5 Notes

In C.5, the primary focus is the Doppler effect. This is the change in frequency of a wave incident on an observer due to the movement of a source or observer. You are expected to understand the Doppler effect for both sound waves and light waves.

For sound waves, two scenarios can occur. First, a sound source moves towards or away from a stationary observer.

1. At position A: As the source moves, a wave is emitted. Since the source is moving, the second wave starts further from the first wave. This decreases the frequency of the wave that A will observe.
2. At position B: As the source moves, a wave is emitted. Since the source is moving, the second wave starts closer to the first wave. This increases the frequency of the wave that B will observe.

Second, an observer moves towards or away from a stationary sound source.

1. At position A: As A moves, a wave is emitted. Since A is moving closer, the second wave is received earlier. This increases the frequency of the wave that A will observe, and the formula for this is:
2. At position B: As B moves, a wave is emitted. Since B is moving further, the second wave is received later. This decreases the frequency of the wave that A will observe, and the formula for this is: