Calculating the Doppler effect

In summary, the conversation discusses finding the velocity of an object based on the frequency shift of soundwaves behind it. One participant suggests using equations relating speed and frequency, while the other mentions the relationship between frequencies in octaves. Ultimately, it is determined that the problem can be solved without using Doppler effect equations by understanding the mathematical relationship between frequencies in octaves.
  • #1
Anabell
2
0

Homework Statement


Given the speed of sound in an environment, c = 300 m/s. We have an object moving with a ceratin velocity. If we know that the soundwaves behind the object are lower by 3 octaves than in front of it, then what is the velocity of the object?

2. Attempt at solving it.
I arrived at the conclusion that if the wavelength of the soundwaves in front of the object is x, then behind it is eight times of that (eg. x*8), since octaves are on a logaritmic scale. I don't know where to go on from here.
 
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  • #2
Where are your equations relating speed to frequency.

You know that f1 = 8 f2, where f1 is the frequency in the front and f2 is the frequency behind.

Plug these into your equations relating speed to frequency, and you should be able to solve for the unknown rest frequency and velocity.
(Two equations and two unknowns.)
 
  • #3
Dr. Courtney said:
Where are your equations relating speed to frequency.

You know that f1 = 8 f2, where f1 is the frequency in the front and f2 is the frequency behind.

Plug these into your equations relating speed to frequency, and you should be able to solve for the unknown rest frequency and velocity.
(Two equations and two unknowns.)
I don't have those equations, could you please ellaborate? :)

Do you mean speed = wavelength * frequency?
 
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  • #4
You must have Doppler effect equations relating speed and frequency shifts for sources moving toward and away.
 
  • #5
Anabell said:

Homework Statement


Given the speed of sound in an environment, c = 300 m/s. We have an object moving with a certain velocity. If we know that the soundwaves behind the object are lower by 3 octaves than in front of it, then what is the velocity of the object?

2. Attempt at solving it.
I arrived at the conclusion that if the wavelength of the soundwaves in front of the object is x, then behind it is eight times of that (eg. x*8), since octaves are on a logarithmic scale. I don't know where to go on from here.
I don't think you need to use Doppler effect equations solve this.

If frequency, fB, is one octave above frequency, fA, then how is fB related to fA mathematically?
 

1. What is the Doppler effect?

The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the source of the wave. It is commonly experienced with sound waves, such as the change in pitch of a siren as it passes by.

2. How is the Doppler effect calculated?

The Doppler effect can be calculated using the formula: Δf/f = v/c, where Δf is the change in frequency, f is the original frequency, v is the velocity of the observer, and c is the speed of the wave.

3. What factors affect the magnitude of the Doppler effect?

The magnitude of the Doppler effect is affected by the relative velocity between the observer and the source, as well as the speed of the wave. Additionally, the angle of incidence and the wavelength of the wave can also impact the magnitude of the effect.

4. How does the Doppler effect apply to different types of waves?

The Doppler effect can be observed in all types of waves, including sound, light, and water waves. For sound waves, it affects the perceived pitch, while for light waves, it affects the perceived color. In water waves, it can cause a change in the direction of the wave.

5. What are some real-world applications of the Doppler effect?

The Doppler effect has various practical applications, such as in weather radar to track the movement of storms, in medical ultrasound to measure blood flow, and in astronomy to determine the speed and direction of celestial objects.

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