The Doppler Effect

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The Doppler Effect

The Doppler Effect

What is the Doppler Effect?



The Doppler Effect is an effect in which an apparant upward shift in frequency is experienced if an observer is moving towards a source or if a source is moving towards an observer. Likewise, an apparant downward shift in frequency is experienced by an observer if he or she is moving away from a source or if the source is moving away from him or her. For example, if an ambulance car moves towards you, the change in frequency causes the pitch to seem higher; whereas when it moves away from you, the pitch seems lower. The Doppler effect applies to color and light as well.

As explained before, when a source approaches an observer, the pitch is higher. When the source recedes from the observer, the pitch is lower. The same concept can be used in astronomy regarding light. Here, the "moving source" is much larger than just an ambulance car; it is an entire galaxy! As the galaxy moves away from us, its light, which is normally white, is shifted down the frequency spectrum towards red. This effect is known as "red shift." Likewise, when a galaxy moves towards us, its light is shifted up the frequency spectrum, producing a "blue shift." Most of the light that reaches us is red, meaning observed galxies are moving away from us. This concept is essential in theorizing cosmic expansion. The Doppler effect gives us knowledge about the rate at which our universe is expanding which helps astronomers predict how old our universe is and how it began to expand, leading to theories such as the "Big Bang."

The Doppler effect is extremely useful in predicting weather. Meteorologists use a stationary transmitter to emit waves toward a moving source. This moving source is some type of precepitation cloud (for example a storm.) The waves emitted by the transmitter hit the storm and bounce back to the station. If the waves that bounce back to the station have a lower frequency, the source (in this case a storm) is moving away from the station because of the Doppler Effect. Likewise, if the waves that have bounced back have a higher frequency than the wave emitted by the transmitter, the meterologists know the storm is moving towards the station. This information can be used to predict the storm's distance, instensity, direction , and speed. The technology used to predict this information using the Doppler effect is called "Doppler Radar." This same method is used to make predictions about tornadoes. The frequencies of waves (that are emitted by Doppler Radar) can indicate high winds and signal if and when a tornado may break. The frequencies that are received after hitting a source are translated into pictures that also indicate the source's speed, direction intensity,distance, etc.


Review of Doppler Applications

Astronomy:-• Cosmic Expansion-• Big Bang Theory-• Describing how Galaxies and Planets move around us

Meteorolgy:-•Detecting precipitation,winds, etc. -•Predicts stroms, tornadoes,etc.-• Describes speed, distance, and direction of source




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