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# The Physics PHYA2 thread! 5th June 2013 watch

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1. (Original post by susanjan123)
Yes however I don't understand how it is positive maximum at a quarter of a period? Thanks

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At half period or 1/2 period, it returns to its original position. (At full period or 1 period, it still returns to its original position as well but the question only asks for the movement within the half period). Basically, a half period is a movement of a point within the half wavelength. The reason why it is max positive at 1/4 period is because........1/2 period=same position. 1/2 divided by 2 is 1/4=max position. Hope this make sense. If not, ask again.
2. (Original post by .raiden.)
Because the wave is oscillating and the points on the wave go up and down? Vibration is perpendicular to travel for transverse
But how do you know it doesn't move downwards?
3. for double slit interference, a single slit comes before the double slit doesn't it?

my main question is whether the path difference is created by the difference in distance between the single slit and the two double slits, OR if the path difference is created by the difference in distance from the two double slits to the screen?
4. (Original post by x-Sophie-x)
Could anyone please explain why the control wire in the Searle's apparatus negates the effect of temperature? I don't understand this :/
you know the spirit level in the searle's apparatus?

basically its held level (so it doesn't slope to one side) by the two wires being the same length, if theres a temperature change, it'll affect both wires, ensuring that the spirit level stays as it is

what I struggle with the searle's apparatus is how to describe everything, like wtf is that blue thing (where the micrometer is shown inside, on the nelson thornes textbook) called?

if we get a 6 marker based on this, is it to just say ''set up a searles apparatus'' and the examiner would get what I mean?
5. Does anyone know where I can find the Jan 2009 paper?
6. (Original post by Me123456789)
Does anyone know where I can find the Jan 2009 paper?
http://www.aqa.org.uk/subjects/scien...d-mark-schemes Opps: sorry, here is jan 2009 paper. here you go.http://papers.xtremepapers.com/AQA/Physics/
7. Thanks.
8. (Original post by Me123456789)
Thanks.
No problem!
9. (Original post by x-Sophie-x)
Could anyone please explain why the control wire in the Searle's apparatus negates the effect of temperature? I don't understand this :/
Yeah basically temperature can cause things to expand, it happens all the time in everyday life with doors and what have you....

Anyways basically what it does to one wire it will do the same to the other. (I *think* however could be wrong, that both wires are made out of same material, it's just that only one has a force exerted on it, so temperature will affect both in the same way.

This just means that you don't get anything added on to you're extension reading because you've had temperature extending it as well.

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10. (Original post by lebron_23)
The first part is simple, you just draw a cuved dotted line above and below the line given to you. Basically two nodes and one antinode. The second part requires you to understand the first part - because you have drawn two of the dotted lines, the wavelength is double the original so you multiply 0.64 by 2 to get 1.28m as your answer.

For part bi you again draw your dotted lines above and below, but this time you have a space of 0.16m between nodes and so you divide 0.64 by 0.16 which gives you four. That tells you that you need to draw 4 half wavelengths, or two full wavelengths.

This stuff is hard to explain so I've attached a picture of what I did when I attempted this question a few days ago.

Attachment 221755

The picture may just be upside down
For bi, its a bit confusing because I thought they would be a total of 4 nodes, but actually there are 5, could you just quickly where I am going wrong?

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11. how do you do jan 12 question 7b?
The wave travels to the right.Describe how the vertical displacement of the knot varies over the next complete cycle
why does the knot go downwards first instead of upwards?
Attached Images

12. (Original post by Jimmy20002012)
For bi, its a bit confusing because I thought they would be a total of 4 nodes, but actually there are 5, could you just quickly where I am going wrong?

Posted from TSR Mobile
Okay, if a string is vibrating such that it has a node X meters from A, the total number of nodes will be the total length of the string, say Y, divided by the distance of X from A (one overtone) plus one.

For example, if I had a string that was 0.5m long and I managed to produce an overtone at 0.1m, then I would have five half wavelengths, but there would be six nodes.

Again, if I had a string of 1m and an overtone at 0.1m, then I would produce ten half wavelengths and I would have eleven nodes.

This perhaps isn't the best way to remember it, as I've basically just made up a sort of formula, but it helps to visualise it. That said, it's quite easy once you draw out the wave. Just remember to divide the original length by the overtone and that's how many half wavelengths you have. Then count the nodes.
13. (Original post by Namige)
I am resitting this, because of the stupid, stupid ISAs.
It screwed me over too
14. (Original post by rainerised)
how do you do jan 12 question 7b?
The wave travels to the right.Describe how the vertical displacement of the knot varies over the next complete cycle
why does the knot go downwards first instead of upwards?
because it says the direction of travel of the waves is from left to right

the knot does NOT move horizontally, it only moves up and down due to the wave passing through it (it follows the vertical displacement of the wave going through it)

as you can see immediately to the left of the knot, there is a trough. If the waves are moving to the right, whatever was on the left of the knot will pass through it. The trough will pass through this knot, making it go down
15. Hi June 2012 4aii i got the right answer but by common sense where actually is that angle on the diagram? Also for bi how did they get 65?
16. on those papers which one is unit 2?
17. (Original post by lebron_23)
Okay, if a string is vibrating such that it has a node X meters from A, the total number of nodes will be the total length of the string, say Y, divided by the distance of X from A (one overtone) plus one.

For example, if I had a string that was 0.5m long and I managed to produce an overtone at 0.1m, then I would have five half wavelengths, but there would be six nodes.

Again, if I had a string of 1m and an overtone at 0.1m, then I would produce ten half wavelengths and I would have eleven nodes.

This perhaps isn't the best way to remember it, as I've basically just made up a sort of formula, but it helps to visualise it. That said, it's quite easy once you draw out the wave. Just remember to divide the original length by the overtone and that's how many half wavelengths you have. Then count the nodes.
Thanks soo much

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18. (Original post by Jack93o)
because it says the direction of travel of the waves is from left to right

the knot does NOT move horizontally, it only moves up and down due to the wave passing through it (it follows the vertical displacement of the wave going through it)

as you can see immediately to the left of the knot, there is a trough. If the waves are moving to the right, whatever was on the left of the knot will pass through it. The trough will pass through this knot, making it go down
ok still don't quite understand why the knot will go down but thanks
19. (Original post by rainerised)
ok still don't quite understand why the knot will go down but thanks

http://www.antonine-education.co.uk/...ves_Page_1.htm

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20. (Original post by rainerised)
ok still don't quite understand why the knot will go down but thanks
imagine a you're on a boat in a lake

if a gentle water wave heads towards you, what happens when the wave passes underneath the boat?

the boat is going to move up and then down

its the same principle with the knot on the string

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