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# Sound wave exam question

1. Q20. Part C (both)

What does "series of maxima and minima" mean?

Paper:
http://www.edexcel.com/migrationdocu...e_20090521.pdf

MS:
http://www.edexcel.com/migrationdocu...7_US021598.pdf

In Part C:
In part A it was a standing wave, and now it's not? WTF path difference? And now we have SEVERAL AND NOT STANDING waves?
Basically, I can't understand anything, could anyone explain?
2. (Original post by Dog4444)
Q20. Part C (both)

What does "series of maxima and minima" mean?

Paper:
http://www.edexcel.com/migrationdocu...e_20090521.pdf

MS:
http://www.edexcel.com/migrationdocu...7_US021598.pdf

In Part C:
In part A it was a standing wave, and now it's not? WTF path difference? And now we have SEVERAL AND NOT STANDING waves?
Basically, I can't understand anything, could anyone explain?
It is still a standing wave.
Info:
For the minima to be zero (the two waves totally cancel out) the waves travelling in opposite directions, the original and reflected, must have the same amplitude.
Can you think of a reason why the original and reflected waves do not have the same amplitude and do not completely cancel out, producing a minimum that isn't zero.
3. (Original post by Stonebridge)
It is still a standing wave.
Info:
For the minima to be zero (the two waves totally cancel out) the waves travelling in opposite directions, the original and reflected, must have the same amplitude.
Can you think of a reason why the original and reflected waves do not have the same amplitude and do not completely cancel out, producing a minimum that isn't zero.
Well, realistically the amplitude goes down as the wave moves, because it loses energy. So, reflected wave has lower amplitude, because it also loses amplitude while getting to the microphone. That's why I don't get how amplitudes get similar.

What's maxima and minima?
4. (Original post by Dog4444)
Well, realistically the amplitude goes down as the wave moves, because it loses energy. So, reflected wave has lower amplitude, because it also loses amplitude while getting to the microphone. That's why I don't get how amplitudes get similar.

What's maxima and minima?
A minima is formed when the sum of the displacements of two overlapping waves is zero.

For example, when a trough and crest overlap the net displacement is zero.

A maxima is when the sum of the displacements is higher (in magnitude) than either two individual displacements.

When two troughs coincide or two crests.
5. (Original post by Ari Ben Canaan)
A minima is formed when the sum of the displacements of two overlapping waves is zero.

For example, when a trough and crest overlap the net displacement is zero.

A maxima is when the sum of the displacements is higher (in magnitude) than either two individual displacements.

When two troughs coincide or two crests.
Oh, ok. It's just nodes and anti-nodes then.

Can anyone explain what's to do with path difference and why amplitudes get similar?
6. (Original post by Dog4444)
Oh, ok. It's just nodes and anti-nodes then.

Can anyone explain what's to do with path difference and why amplitudes get similar?
http://www.physicsclassroom.com/class/light/u12l3b.cfm
7. I know what it is, but I don't understand how it works here.
We don't know the length of sound wave, we don't know the distance between loudspeaker and metal.
Could you just explain what to do with path difference (and path difference between what? Reflected wave and original one or what?) and how similar amplitudes come up?
8. The reflected wave will have lost some energy during transmission. Since its energy has fallen so will its amplitude.

Therefore, at a particular point where a crest and trough overlap the magnitude of one of those is not enough to COMPLETELY cancel the other.

Hence, full cancellation does not occur and a minima with value zero isnt formed.
9. (Original post by Ari Ben Canaan)
The reflected wave will have lost some energy during transmission. Since its energy has fallen so will its amplitude.

Therefore, at a particular point where a crest and trough overlap the magnitude of one of those is not enough to COMPLETELY cancel the other.

Hence, full cancellation does not occur and a minima with value zero isnt formed.
Why in PART A then it varies through series of maxima and minima? You said they can't completely cancel each other.
And I still can't see what to do with path difference and why amplitudes get SIMILAR.
10. (Original post by Dog4444)
Why in PART A then it varies through series of maxima and minima? You said they can't completely cancel each other.
And I still can't see what to do with path difference and why amplitudes get SIMILAR.
Firstly, I dont know why you're going on and on about path differences.

Secondly, in part(a) you assume an ideal standard wave that witnesses no decreases in energy during transmission.
11. (Original post by Ari Ben Canaan)
Firstly, I dont know why you're going on and on about path differences.

Secondly, in part(a) you assume an ideal standard wave that witnesses no decreases in energy during transmission.
Well, it's on a mark scheme.

"As the microphone moves towards the plate, the path
difference decreases "

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