Profile
Settings
Refer your friends
Sign out
When the source and observer are moving relative to each other, the frequency observed by the observer (fa) is different from the actual frequency produced by the source (f0). This is the definition of the Doppler effect in Physics. Here, when the source of waves is moving towards the observer, they will have an upward frequency shift.
As for the observers from whom the source is receding. In contrast, waves emitted by a source travelling away from an observer get stretched out. The drop-in pitch of ambulance sirens as they pass by and the shift in red light are common examples of the Doppler Effect.
In astronomy, that source can be a star that emits electromagnetic waves; from our vantage point, the Doppler effect occurs as the star orbits around its centre of mass and moves toward or away from Earth. These wavelength shifts can be witnessed as simple changes in its spectrum, the rainbow colours released in light. When a star comes towards us, its wavelengths are flattened, and its spectrum becomes slightly bluer. When the star moves away from us, its spectrum looks slightly redder.
Planetary scientists use a high- revolutionised prism-like instrument, spectrograph, to witness the red and blue shifts over time. Spectrograph separates charging light waves into different colours.
In every star’s outer layer, some atoms absorb light at specific wavelengths, and this absorption appears as dark lines in the different colours of the star’s spectrum that are recorded from the light emanating from the star. Researchers use variations in these lines as complying markers to measure the size of the Doppler effect.
The general formula of the Doppler Effect is:
F = (c ±vr / c ±vs) fo
Where,
c = propagation speed of waves in the medium;
vr = speed of the receiver relative to the medium, +c if the receiver is moving towards the source, -c if the receiver is moving away.
vc = speed of the source relative to the medium, +c if the source is moving away -c if the source is moving towards the receiver.
There is the main Doppler effect equation. However, this equation can change in different situations. It is adjusted or modified depending on the velocities of the observer or the source of the sound.
Why Do We Observe the Doppler Effect?
The main reason we experience the Doppler effect is the wave source moving toward the observer. Each new wave crest formed from the source is emitted from a location closer to the observer. Therefore, as the source moves closer, the waves will now take less time to reach the observer or the time between the arrivals of new wave crests is reduced.
This further causes an increase in frequency. Similarly, when the source of waves is going away, the waves are emitted from a farther location, thus increasing the arrival time between each new wave. This leads to a decrease in frequency.
Uses of dopplers effect
- Astronomy
- Radars
- Sirens
- Satellites
- Audio
- Vibration measurement
- Medical imaging and blood flow management
Conclusion
We all have experienced the Doppler effect. For example, if you are standing on a road corner and an ambulance approaches with its siren blaring, the sound of the siren steadily gains its pitch as it comes closer. Doppler effect is defined as the change in the observed frequency of a wave when the source of the wave is moving with respect to the observer. The Doppler effect, which occurs both in sound and electromagnetic waves—including light waves—has several applications.
Astronomers use it, for instance, to gauge the movement of stars relative to Earth. Closer to home, principles relating to the Doppler effect find application in radar technology. Doppler radar provides information concerning weather patterns, but some people experience it less pleasantly: when a police officer uses it to measure their driving speed before writing a ticket.
