physics 101 learning object 2

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The Doppler Effect Question 1) We are looking at a stationary source emitting waves, in this case we will say that it is a stone on a string in a pool of water being bobbed up and down once per second (frequency). On the left side of the pool is point A and on the right is point B. Circle one: Will the waves reach point A first, point B first, or at same time? Answer: At the same time because the stone is not moving towards point A or B, the frequency at which the waves will arrive at the point will be the same for both points. Furthermore the frequency at points A and B will be the same as the frequency produced by the bobbing stone (one bob per second). Question 2) We are looking at a moving source emitting waves, in this case it is a stone on a string in a pool of water being bobbed up and down at a frequency of one bob per second. As the stone bobs it is also moving left towards point A and away from point B. Circle one: A) Is the frequency higher at point A, Point B, or same for points A and B? B) Does the frequency of the stone change? Yes or No? Stone on string Point A ------- ------Point B

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Page 1: Physics 101 learning object 2

The Doppler Effect

Question 1) We are looking at a stationary source emitting waves, in this case we will say that it is a stone on a string in a pool of water being bobbed up and down once per second (frequency). On the left side of the pool is point A and on the right is point B. Circle one: Will the waves reach point A first, point B first, or at same time?

Answer: At the same time because the stone is not moving towards point A or B, the frequency at which the waves will arrive at the point will be the same for both points. Furthermore the frequency at points A and B will be the same as the frequency produced by the bobbing stone (one bob per second).

Question 2) We are looking at a moving source emitting waves, in this case it is a stone on a string in a pool of water being bobbed up and down at a frequency of one bob per second. As the stone bobs it is also moving left towards point A and away from point B. Circle one:

A) Is the frequency higher at point A, Point B, or same for points A and B?B) Does the frequency of the stone change? Yes or No?

------Point BPoint A -------

Stone on string

Stone on string

Point A ------- ------Point B

Page 2: Physics 101 learning object 2

Answer: A) The frequency is higher at point A. This is because as the stone moves towards A, the distance that each of the waves has to travel is shorter and shorter thus the waves reach A faster. The opposite can be said for point B. As the stone moves away from point B, the distance of each wave gets farther and farther away and thus takes more time therefore the frequency at point B is lower. B) The frequency of the stone does not change throughout its movements, it stays constant the whole time (one bob per second).

Question 3) Two people are standing on the street (person A and person B). An ambulance with its sirens on is driving towards person B and thus away from person A. Circle one: Is the noise greater for person A, person B, or same for both? (Picture is of frequency of sound waves in birds eye view)

Answer: Because the ambulance is driving towards person B this means that the frequency of the sound waves is higher for person B and lower for person A. Small wavelengths closer to person B mean high frequency and larger wavelengths closer to person A mean low frequency. A higher frequency of sound means that the sound is greater and therefore the sound would be greater for person B.

Ambulance with sirens on

Person A -------

------Person B