The Doppler Effect is one of the concepts that will be discussed and elaborated on in your school and Physics tuition learning. It is a natural phenomenon in which an observer who is moving towards or away from the source of a wave experiences a discernible change in the frequency (or wavelength) of a wave. You must be familiar with the changes in the pitch of an ambulance’s siren as the ambulance approaches you, passes by you and then goes away from you. That is because of the Doppler Effect.

The Doppler Effect can be observed (or experienced) in all kinds of waves, including sound wave, light wave and water wave. Here is an example to better understand how it works.

Suppose that a dragonfly has fallen in the middle of a pond and is fluttering its wings in desperation. The disturbances created by the dragonfly’s wings travel outward through the water in concentric circles called ripples. These circles travel at the same speed and reach the edge of the pond at the same frequency that the dragonfly is producing the disturbances. Let’s say that the dragonfly is producing the disturbances at a frequency of 3 disturbance per second. If you are standing at the edge of the pond, you will see the circles approaching you at the frequency of 3 disturbance per second.

Now, let’s suppose that the dragonfly is moving towards the opposite edge of the pond (from where you are standing) where a friend of yours is standing. Since the dragonfly is moving towards your friend, each consecutive disturbance that originates from a position that is farther away from you and closer to your friend. This means that the circles take less time to reach your friend than you. Consequently, the frequency observed by your friend is higher than the frequency you have observed.

The net effect of the motion of the dragonfly is that your friend observes a frequency that is higher than the frequency at the source and you observe a frequency that is lower than the frequency at the source. This is why you hear three different pitches of the siren when an ambulance is approaching you, when it is near you and when it is going away from you.

Why do we experience the Doppler Effect? When the source of the waves is getting closer to the observer (or vice versa), the distance between the crest of successive waves becomes increasingly smaller, which means that each wave reaches the observer in less time than the previous wave. Thus, the observer observes a higher frequency.

Conversely, when the source of the wave is moving away from the observer, the distance between the crest successive waves becoming increasingly larger. As a result, each wave reaches takes longer than the previous wave to reach the observer. Thus, the observer observes a lower frequency.

You can observe this phenomenon not only when the source of the wave is moving towards or away from you, but also when you are moving towards or away from it. Thus, the Doppler Effect can be observed when the waves are moving, when the observer is moving or when the medium is moving. If you want to learn the mathematics behind the Doppler Effect, we suggest that you talk to a good physics tuition teacher and understand how it is applicable in our daily lives.