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Creating a Visual Doppler

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The objective of the experiment is to create the visual model of what happens to sound waves when a car passes by us.  

Materials Required:

  • Two different color pieces of any colored paper
  • Ruler
  • Scissors
  • Cello tape
  • A small toy car
  • Some blank papers and a pencil/ or  a camera

Procedure:

  • Cut one color paper in five strips (an inch wide each), with the longest strip of 11 inches and rest all an inch shorter than the previous one. For instance, if the longest strip is 11 inches long, then others will be 10”, 9”, 8” and 7,” respectively.
  • Now join every strip at its end with glue, so that you get five loops of different sizes.
  • Place the car in the center of the second construction paper and fix the five loops around the car. Make sure that the loops are neither touching the car nor each other and have equal distance between them.
  • The loops here represent sound waves and show how sound waves travel outward from the car engine when the automobile is absolutely still.
  • Draw a picture/take a photo of the car and the loops representing the still position (you may even glue everything as it is and make another model for the second part of the experiment).
  • Now gently roll/move the car forward till it pushes the set of loops further in a way that they touch each other at a point.

Observation:

  • When the car moves in front, the loops representing sound waves also move and get compressed or squished together. This is the reason we hear a high-pitched sound when a car is coming towards us, while the waves behind the car are stretched out, making a low-pitch sound.
  • This is the Doppler Effect!
  • If you look at the two models of the car in standing and moving position, you will notice how the sound waves get affected by the movement of the car.

Explanation:

The Doppler Effect can though be observed in any type of wave i.e. sound wave, water wave or even light wave, but we are most familiar with Doppler Effect in sound waves. A perfect example for this is when we hear the siren of a police van or an emergency vehicle coming towards us and then going away. As the vehicle approaches, the siren is the loudest but after passing by, the siren sound decreases gradually. The Doppler Effect is nothing but the apparent shift in the frequency of any sound wave, which is produced by a moving source.

Uses:

  • The Doppler Effect finds great interest among astronomers who use the information regarding shift in the frequency of  electromagnetic waves, which are produced by moving stars both in our galaxy and beyond. This helps them in driving information about stars and the galaxy.
  • In fact, with the help of the Doppler Effect, any specific information of stars in the galaxy can be determined easily. The electromagnetic radiation emitted by stars in the galaxy will show a red shift i.e. frequency shifted downward in case the star rotates within the cluster in the direction away from earth. However, if the star rotates in the direction towards the earth, it will show a blue shift, confirming an upward shift in the respective frequency.

Image Credit: freedigitalphotos.net

 

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