Chapter 25, Problem 44A

Would it be correct to say that the Doppler effect is the apparent change in the speed of a wave due to the motion of the source? (Why is this question a test of reading comprehension as well as a test of physics?)

To determine

To explain: Whether it is correct to say that Doppler Effect is the apparent change in the speed of a wave.

Answer to Problem 44A

It is incorrect to say that the Doppler Effect is the change in the speed of a wave but it is the apparent change in the frequency of the wave observed due to the motion of the source, observer, or both. It requires a basic understanding of terms like frequency, velocity, Doppler Effect. This question is a test of both.

Explanation of Solution

Introduction:

Doppler Effect is the phenomenon of measuring the observed frequency of the sound waves generated by the source when either source or the observer or both are in motion.

When a source or observer moves towards or away each other, then sound waves emitted by source are received by observer. Observing frequency of such sound waves is known as Doppler Effect. In this phenomenon, the speed of sound waves remains constant. The only thing here variable is the frequency and wavelength of the sound waves received.

If source moves towards the stationary observer or observer move towards the stationary source, then frequency of sound observed is higher. If source moves away, the frequency of sound waves observed is lesser. But, in any scenario, the speed of sound waves remains constant.

Conclusion:

It is a myth that the speed of sound waves changes in the Doppler Effect. In reality, it is the apparent change in the frequency due to the position and motion of source and observer. To explain such a concept, meaning of frequency, speed of sound must be known.