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10.2 Periodic Waves

2 min readjune 7, 2020

Peter Apps

Peter Apps

Peter Apps

Peter Apps

Enduring Understanding 6.B 👨‍💻

A is one that repeats as a function of both time and position and can be described by its , , , , and .

Essential Knowledge 6.B.1 🏘

For a , the is the repeat time of the wave. The is the number of repetitions of the wave per unit time.

Essential Knowledge 6.B.2 🏘

For a , the is the repeat distance of the wave.

Essential Knowledge 6.B.4 🏘

For a , is the ratio of over .

Essential Knowledge 6.B.5 🏘

The of a wave depends on the of source and observer.

Relationship between and

As we saw above, the velocity of a wave is related to the wave’s and the . As long as the velocity is constant, the and have an inverse relationship (when one increases, the other decreases by the same factor).

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-iZ92benloWk5.gif?alt=media&token=1b3a20c7-5076-4c45-a9d1-7096081924df

Image courtesy of Blog.Soton.

In this image we see that the longer corresponds to a smaller (longer time between peaks) and the shorter causes the to increase. In both cases, the velocity of the wave is the same.

Moving Sources of Waves

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-20%20at%208.42-zCIUGdn8HILm.png?alt=media&token=61b3cc30-8108-49b7-ab90-0e50aae4ced6

When a source of waves is in motion relative to an observer, the observed and of the waves change. This effect is known as the and basically results in the appearing to be higher when the source is moving towards the observer and lower when the source is moving away. (The change in wavelengths is the opposite of this trend, since and wavelengths are indirectly related.) The actual amount of shift in the depends on the of the object and observer, but in general faster speeds lead to higher frequencies.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-20%20at%208.43-q65iX5cYuutY.png?alt=media&token=0e929f9f-afbc-4045-ac8b-f9dcf1a1af83

The graph above shows a wave-source moving towards and then passing an observer. Notice the sudden shift in when the source switches from moving towards to moving away from the observer.

** Note - There are mathematical equations for modelling the , and this effect also applies to light and other Electromagnetic waves too. However AP 1 will only test you on mechanical waves and qualitative relationships.

🎥Watch: AP Physics 1 - Unit 10 Streams

Key Terms to Review (10)

Amplitude

: The amplitude represents the maximum displacement from equilibrium in a periodic motion.

Doppler Effect

: The Doppler Effect is the change in frequency or wavelength of a wave as observed by an observer moving relative to the source of the wave. It occurs when there is relative motion between the source and the observer.

Energy

: The ability to do work or cause change.

Frequency

: Frequency is the number of complete cycles or oscillations that occur in one second. It affects how many times an object vibrates back and forth within a given time period.

Observed Frequency

: The observed frequency refers to the frequency at which an observer perceives a sound wave or light wave due to relative motion between the source and observer.

Period

: The period refers to the time it takes for one complete cycle of a repeating event or motion.

Periodic Wave

: A periodic wave is a type of wave that repeats itself in both time and space. It has a consistent pattern and can be described by its amplitude, frequency, and wavelength.

Relative Motion

: Relative motion refers to the movement of one object with respect to another object, taking into account their velocities and directions.

Speed

: The rate at which an object moves or changes position over time.

Wavelength

: The distance between two consecutive points on a wave that are in phase, such as from crest to crest or trough to trough.

10.2 Periodic Waves

2 min readjune 7, 2020

Peter Apps

Peter Apps

Peter Apps

Peter Apps

Enduring Understanding 6.B 👨‍💻

A is one that repeats as a function of both time and position and can be described by its , , , , and .

Essential Knowledge 6.B.1 🏘

For a , the is the repeat time of the wave. The is the number of repetitions of the wave per unit time.

Essential Knowledge 6.B.2 🏘

For a , the is the repeat distance of the wave.

Essential Knowledge 6.B.4 🏘

For a , is the ratio of over .

Essential Knowledge 6.B.5 🏘

The of a wave depends on the of source and observer.

Relationship between and

As we saw above, the velocity of a wave is related to the wave’s and the . As long as the velocity is constant, the and have an inverse relationship (when one increases, the other decreases by the same factor).

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-iZ92benloWk5.gif?alt=media&token=1b3a20c7-5076-4c45-a9d1-7096081924df

Image courtesy of Blog.Soton.

In this image we see that the longer corresponds to a smaller (longer time between peaks) and the shorter causes the to increase. In both cases, the velocity of the wave is the same.

Moving Sources of Waves

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-20%20at%208.42-zCIUGdn8HILm.png?alt=media&token=61b3cc30-8108-49b7-ab90-0e50aae4ced6

When a source of waves is in motion relative to an observer, the observed and of the waves change. This effect is known as the and basically results in the appearing to be higher when the source is moving towards the observer and lower when the source is moving away. (The change in wavelengths is the opposite of this trend, since and wavelengths are indirectly related.) The actual amount of shift in the depends on the of the object and observer, but in general faster speeds lead to higher frequencies.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-20%20at%208.43-q65iX5cYuutY.png?alt=media&token=0e929f9f-afbc-4045-ac8b-f9dcf1a1af83

The graph above shows a wave-source moving towards and then passing an observer. Notice the sudden shift in when the source switches from moving towards to moving away from the observer.

** Note - There are mathematical equations for modelling the , and this effect also applies to light and other Electromagnetic waves too. However AP 1 will only test you on mechanical waves and qualitative relationships.

🎥Watch: AP Physics 1 - Unit 10 Streams

Key Terms to Review (10)

Amplitude

: The amplitude represents the maximum displacement from equilibrium in a periodic motion.

Doppler Effect

: The Doppler Effect is the change in frequency or wavelength of a wave as observed by an observer moving relative to the source of the wave. It occurs when there is relative motion between the source and the observer.

Energy

: The ability to do work or cause change.

Frequency

: Frequency is the number of complete cycles or oscillations that occur in one second. It affects how many times an object vibrates back and forth within a given time period.

Observed Frequency

: The observed frequency refers to the frequency at which an observer perceives a sound wave or light wave due to relative motion between the source and observer.

Period

: The period refers to the time it takes for one complete cycle of a repeating event or motion.

Periodic Wave

: A periodic wave is a type of wave that repeats itself in both time and space. It has a consistent pattern and can be described by its amplitude, frequency, and wavelength.

Relative Motion

: Relative motion refers to the movement of one object with respect to another object, taking into account their velocities and directions.

Speed

: The rate at which an object moves or changes position over time.

Wavelength

: The distance between two consecutive points on a wave that are in phase, such as from crest to crest or trough to trough.


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© 2024 Fiveable Inc. All rights reserved.

AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.