10.2 Periodic Waves
2 min read•june 7, 2020
Peter Apps
Peter Apps
Enduring Understanding 6.B 👨💻
A periodic wave is one that repeats as a function of both time and position and can be described by its amplitude, frequency, wavelength, speed, and energy.
Essential Knowledge 6.B.1 🏘
For a periodic wave, the period is the repeat time of the wave. The frequency is the number of repetitions of the wave per unit time.
Essential Knowledge 6.B.2 🏘
For a periodic wave, the wavelength is the repeat distance of the wave.
Essential Knowledge 6.B.4 🏘
For a periodic wave, wavelength is the ratio of speed over frequency.
Essential Knowledge 6.B.5 🏘
The observed frequency of a wave depends on the relative motion of source and observer.
Relationship between frequency and wavelength
As we saw above, the velocity of a wave is related to the wave’s frequency and the wavelength. As long as the velocity is constant, the frequency and wavelength have an inverse relationship (when one increases, the other decreases by the same factor).
Image courtesy of Blog.Soton.
In this image we see that the longer wavelength corresponds to a smaller frequency (longer time between peaks) and the shorter wavelength causes the frequency to increase. In both cases, the velocity of the wave is the same.
Moving Sources of Waves
When a source of waves is in motion relative to an observer, the observed wavelength and frequency of the waves change. This effect is known as the Doppler Effect and basically results in the frequency 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 frequency and wavelengths are indirectly related.) The actual amount of shift in the frequency depends on the speed of the object and observer, but in general faster speeds lead to higher frequencies.
The graph above shows a wave-source moving towards and then passing an observer. Notice the sudden shift in frequency when the source switches from moving towards to moving away from the observer.
** Note - There are mathematical equations for modelling the Doppler Effect, 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 read•june 7, 2020
Peter Apps
Peter Apps
Enduring Understanding 6.B 👨💻
A periodic wave is one that repeats as a function of both time and position and can be described by its amplitude, frequency, wavelength, speed, and energy.
Essential Knowledge 6.B.1 🏘
For a periodic wave, the period is the repeat time of the wave. The frequency is the number of repetitions of the wave per unit time.
Essential Knowledge 6.B.2 🏘
For a periodic wave, the wavelength is the repeat distance of the wave.
Essential Knowledge 6.B.4 🏘
For a periodic wave, wavelength is the ratio of speed over frequency.
Essential Knowledge 6.B.5 🏘
The observed frequency of a wave depends on the relative motion of source and observer.
Relationship between frequency and wavelength
As we saw above, the velocity of a wave is related to the wave’s frequency and the wavelength. As long as the velocity is constant, the frequency and wavelength have an inverse relationship (when one increases, the other decreases by the same factor).
Image courtesy of Blog.Soton.
In this image we see that the longer wavelength corresponds to a smaller frequency (longer time between peaks) and the shorter wavelength causes the frequency to increase. In both cases, the velocity of the wave is the same.
Moving Sources of Waves
When a source of waves is in motion relative to an observer, the observed wavelength and frequency of the waves change. This effect is known as the Doppler Effect and basically results in the frequency 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 frequency and wavelengths are indirectly related.) The actual amount of shift in the frequency depends on the speed of the object and observer, but in general faster speeds lead to higher frequencies.
The graph above shows a wave-source moving towards and then passing an observer. Notice the sudden shift in frequency when the source switches from moving towards to moving away from the observer.
** Note - There are mathematical equations for modelling the Doppler Effect, 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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