Doppler effect and frequency of the horn

In summary, John is listening to a horn with a frequency of 300 Hz when both he and the horn are at rest. If he hears a pitch of 330 Hz, the possible scenarios are: both can be moving at different speeds, John can be moving towards the horn, and both can be moving in opposite directions. The pitch is proportional to frequency and is determined by the relative velocities of the source and listener. The correct answers are B, C, and F, or ABCF. The difference between speed and velocity is that speed is a scalar, while velocity is a vector with both magnitude and direction.
  • #1
Naldo6
102
0
John is listening to a horn. He knows the frequency of the horn is 300 Hz when both he and the horn are at rest. If he hears a pitch of 330 Hz, there are clearly several possibilities. (Give ALL correct answers, i.e., B, AC, BCD...)

A) Both can be moving and have the same speed.
B) Both can be moving and have different speeds.
C) John is moving towards the horn at rest.
D) The distance between John and the horn is increasing with time.
E) Both cannot be moving in the same direction.
F) Both can be moving, in opposite directions.

I select B,C,F and get the wrong answer... why?... can anyone help me?...

is the pitch inverse to the frecuecy or proportional?...
 
Physics news on Phys.org
  • #2
The pitch is proportional to frequency, so we want to have the cases where John hears a higher frequency than the actual frequency. When does that happen?
 
  • #3
Imagine yourself standing right next to a moving train, does the horn sound high pitched when you are close to train or away from train. Just turn on some music and move your head towards and away from the source of music. You'll get your answer then.
And btw, frequency and wavelength are inversely proportional.
 
  • #4
ok, when both are moving at the same speed, it can't be, but when moving with diferrent speed iti coulb be, when john is moving towards the horn the pitch is going to be going up so it could be, when the distance betwenn them is increasing the frequency is going down so it is not an option, when both are moving in the same or oposite direction it depends on their velocities right?...

so i know that the answer B and C are correct but i don't know if it is also the E or the F
 
  • #5
Right then, notice that F implies D... if two bodies are moving in opposite directions, their distance must increase. As for E, chew on this... exactly what determines the frequency in the Doppler effect, relative velocity or direction of travel?
 
  • #6
so the correect answer is BCE... right?..those are the three posibilities?...
 
  • #7
May I ask for your justification for option E?
 
  • #8
direction on travel... if the source and observer moves towards the frequency goes up but if the source and the observer go away the frequency decrease... right?...
 
  • #9
Ah, I see where your confusion lies... actually it's not as simple as saying that it is determine by them moving towards each other or otherwise.

Doppler's effect is actually determined by the relative speeds of the source and listener. If the listener is approaching the source with respect to the frame of the source, then the frequency heard by the listener increases. This could happen in two cases... can you identify them?
 
  • #10
i really don't understand... too much but my answer B and C are correct, but there is any other option that is correct too?... which is?...
 
  • #11
B and C are definitely correct. If this is a web assignment, check the formatting for your initial answer B, C and F, which should be inputted as BCF. F can hold true, if the source and the listener are approaching each other (I made a mistake earlier regarding the F implying D, I'm so sorry). My answer would be BCF, then , your original answer, but if the formatting was correct, then try BC only.
 
  • #12
i have tried BCF, BC, and give me the wrong answers... i also tried the BCEF and is still wrong.. it shuold have another posibility that we are not thinking about...
 
  • #13
Oh dear, I think I finally got it. Option A says same SPEED. Yes, they can have the same speed but different velocities, i.e they can be moving towards each other at the same speed. I completely missed that point. ABCF... that should be it. I'm so sorry I missed that out completely.
 
  • #14
ok thanks that was the correct answer but what is the diference betwenn speed and velocity?..
 
  • #15
Speed is a scalar, meaning that it is only the magnitude, regardless of direction. Two objects may have the same speed but may move in two completely different directions, i.e. possibly towards each other or away from each other or any other combination.

Velocity is a vector, meaning that it has both magnitude and direction... Two objects of the same velocity must have the same speed and same direction, and their separation must be constant.
 
  • #16
oh ok thanks...a lot
 

FAQ: Doppler effect and frequency of the horn

1. What is the Doppler effect?

The Doppler effect is the perceived change in frequency of a wave due to the relative motion between the source of the wave and the observer.

2. How does the Doppler effect affect the frequency of a horn?

The Doppler effect causes the frequency of a horn to appear higher to an observer if the horn is moving towards them, and lower if the horn is moving away from them.

3. What factors influence the magnitude of the Doppler effect on the frequency of a horn?

The magnitude of the Doppler effect on the frequency of a horn is influenced by the speed of the horn, the speed of the observer, and the medium through which the sound wave travels.

4. Can the Doppler effect change the pitch of a horn?

Yes, the perceived change in frequency caused by the Doppler effect can change the pitch of a horn to the observer. This is why the sound of a passing car horn changes as it passes by.

5. How is the frequency of a horn affected if the source and observer are moving in the same direction?

If the source and observer are moving in the same direction, the frequency of the horn will not be affected significantly by the Doppler effect. The perceived change in frequency will be minimal or imperceptible.

Similar threads

Doppler effect and beat frequency
Replies
3
Views
2K
Travelling towards a Canyon Wall: Calculating Beat Frequency
Replies
3
Views
1K
Range of frequency heard by observer related to Doppler effect
Replies
8
Views
562
Calculating frequencies with the Doppler Effect
Replies
1
Views
3K
What Causes the Doppler Shift John Experiences?
Replies
3
Views
7K
How do you calculate wind speed using the Doppler effect?
Replies
4
Views
3K
Beats calculation/Doppler Effect
Replies
1
Views
2K
Where Can I Find Doppler Effect Sound Samples for Specific Scenarios?
Replies
1
Views
2K
Speed of Cars with the Doppler Effect
Replies
1
Views
2K
Doppler Effect; Two Moving Objects
Replies
4
Views
6K

Hot Threads

Recent Insights

Back
Top