Beat Frequencies

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# Beat Frequencies - PowerPoint PPT Presentation

Beat Frequencies. Assume two waves are superpositioned Amplitudes are the same Frequencies & wavelengths are different Use fact that. to yield. Groups and phases. Cosine portion defines “envelope” within which sine portion oscillates Envelope moves with a speed.

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## PowerPoint Slideshow about 'Beat Frequencies' - Sophia

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Presentation Transcript
Beat Frequencies
• Assume two waves are superpositioned
• Amplitudes are the same
• Frequencies & wavelengths are different
• Use fact that

to yield

Groups and phases
• Cosine portion defines “envelope” within which sine portion oscillates
• Envelope moves with a speed
• Individual sine waves move with a speed of
• As frequencies get closer together, beat frequency goes down
• Beat frequencies are often used with Doppler shifts to determine speed

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You have two tuning forks that have a beat frequency of 2 Hz with respect to each other. One of them has a frequency of 440 Hz, but you do not know the frequency of the other. You place a small piece of clay on the other, an amount just capable of changing the beat frequency by 1 Hz, and you repeat the experiment. This time the beat frequency is 3 Hz. From this information, what is the frequency of the other tuning fork (when it has no clay on it)?

• 442 Hz.
• 443 Hz.
• 438 Hz.
• 437 Hz.

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You have two tuning forks that have a beat frequency of 2 Hz with respect to each other. One of them has a frequency of 440 Hz, but you do not know the frequency of the other. You place a small piece of clay on the other, an amount just capable of changing the beat frequency by 1 Hz, and you repeat the experiment. This time the beat frequency is 3 Hz. From this information, what is the frequency of the other tuning fork (when it has no clay on it)?

• 442 Hz.
• 443 Hz.
• 438 Hz.
• 437 Hz.
A beat frequency of 150 Hz is produced by an ultrasonic echo mixed with its original frequency of 2.50 MHz after being reflected from the heart wall of a patient. What is the speed of the wall? Take the speed of sound in the body as being1540 m/s.

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