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# Edexcel Physics Unit 2 - Waves

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1. I am in the process of preparing for my edexcel unit 2 physics exam. I recently did a past paper but there was one kind of question that i didn't understand. It asked you to draw an arrow to show in which direction a point on a wave was about to move. The questions I am talking about are 12b) and 17aii) on the jan 2009 paper. There is a link to it here https://docs.google.com/viewer?a=v&q...VV0tKu_KWCZJBA.

One other question that i didn't and still don't fully understand is question 13b). I would be really grateful if someone could tell me how to answer these questions. Thank You.
2. Please can someone help me. I will give rep to anyone that can explain it to me.
3. I'm doing aqa so i'm not really sure not seen this style of paper but I think it is trying to show that the individual particles will be moving perpendicular to direction of wave.
4. (Original post by laurenb11)
I'm doing aqa so i'm not really sure not seen this style of paper but I think it is trying to show that the individual particles will be moving perpendicular to direction of wave.
But how can you tell whether it would be vertically upwards or vertically downwards? Also, can you help me on the current question (question 13). Thank you.
5. for 12b) will be moving vertically upwards, i think, as the next adjacent particle is highier? gives impression its in phase.
for 13)a)ii) i would say same thing looking at the place next to it? im not sure this is the correct way but surely y shall be vertically upwards and z would be vertically downwards as its in phase with x.

and about the current one, im really sure what its asking, but a coloumb is an amp per second so an As (amp sec)
I dont know how to the second part without my notes (revision isnt going to well :/)
6. (Original post by laurenb11)
for 12b) will be moving vertically upwards, i think, as the next adjacent particle is highier? gives impression its in phase.
for 13)a)ii) i would say same thing looking at the place next to it? im not sure this is the correct way but surely y shall be vertically upwards and z would be vertically downwards as its in phase with x.

and about the current one, im really sure what its asking, but a coloumb is an amp per second so an As (amp sec)
I dont know how to the second part without my notes (revision isnt going to well :/)
I looked at the mark scheme and it said the answer was vertically downwards (for question 12). But the directions for y and Z are the same as what you said. And for question 13 I could do the first part, it was the second part i needed help with. So I think I understand how to do question 17 (the one with y and z), but you weren't given a direction at any point on question 12 so although it is in phase, you still don't know which direction it is travelling in.Thank you for your reply.
7. Bump!
8. (Original post by brittanna)
Bump
for 13b is he answer 10, 5 and 30 respectively?
9. (Original post by Emissionspectra)
for 13b is he answer 10, 5 and 30 respectively?
Yes, it is. Please can you tell me how you got that, and also, if you know it, the answers to questions 17 and 12. Thank You.
10. Wow, I'm not the only one who struggles to understand these bloody questions and mark schemes.

I can't understand Q12 either. Part B it's in equilibrium, so it doesn't move? And how in Part C the water surface is at rest at max displacement?
11. (Original post by brittanna)
So I think I understand how to do question 17 (the one with y and z)
Could you explain?

What's the difference between Y and Z? They're on the same "arc" and it goes up so all the points on this "arc" go up as well?
12. (Original post by brittanna)
Yes, it is. Please can you tell me how you got that, and also, if you know it, the answers to questions 17 and 12. Thank You.
For question 17 Y will move up as its in antiphase and Z will move down its in phase with X. For question 13 for I3 there has to be the same current leaving the circuit as entering it so therefore has to be 30mA for I1 if you look at where the current first enters its 30mA 20 mA goes up one branch so therefore 10mA must go down the other branch, as you cant suddenly have less current. For I2 the 15mA going through the bulb and the current of I1 will meet up and then travel towards the end of the circuit this is 25mA therefore the remaining curent must be 5mA
13. (Original post by Emissionspectra)
Z will move down its in phase with X.

Is it? The distance between X and Z is clearly less than a wavelength.
14. (Original post by Emissionspectra)
For question 17 Y will move up as its in antiphase and Z will move down its in phase with X. For question 13 for I3 there has to be the same current leaving the circuit as entering it so therefore has to be 30mA for I1 if you look at where the current first enters its 30mA 20 mA goes up one branch so therefore 10mA must go down the other branch, as you cant suddenly have less current. For I2 the 15mA going through the bulb and the current of I1 will meet up and then travel towards the end of the circuit this is 25mA therefore the remaining curent must be 5mA
Thank You, and what about Question 12, you weren't given an initial direction at any point on the wave. So how are you meant to know which direction it is travelling in at the point given?
15. (Original post by Dog4444)

Is it? The distance between X and Z is clearly less than a wavelength.
Oh yeah, I didn't notice that. Hmmmm. I just really hate all of these types of questions.
16. Hi

That question on the current junctions required some prior knowledge on Kirchoff's first law
'At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node'.

So you can deduce that for I1 the 20amp current + xamp current = 30amps so x=10amps

And for i2 you can deduce that 20amps = 15amps + xamps so x=5amps

And for i3 it is simply the same as the current which which flowing prior to the massive mess of a current juction which is 30amps.

Hope that was helpful
17. (Original post by MathMan)
Hi

That question on the current junctions required some prior knowledge on Kirchoff's first law
'At any node (junction) in an electrical circuit, the sum of currents flowing into that node is equal to the sum of currents flowing out of that node'.

So you can deduce that for I1 the 20amp current + xamp current = 30amps so x=10amps

And for i2 you can deduce that 20amps = 15amps + xamps so x=5amps

And for i3 it is simply the same as the current which which flowing prior to the massive mess of a current juction which is 30amps.

Hope that was helpful
I don't suppose you know how to obtain the answers to questions 12 and 17. It's just really annoying me because they seem like marks that are so simple to get and only require a simple understanding of waves, and yet i still can't answer them.
18. (Original post by brittanna)
I don't suppose you know how to obtain the answers to questions 12 and 17. It's just really annoying me because they seem like marks that are so simple to get and only require a simple understanding of waves, and yet i still can't answer them.
http://www.edexcel.com/migrationdocu...2_US020961.pdf

"candidates, who correctly identified that
the water at Y was moving upwards"

**** edexcel.
19. (Original post by Dog4444)
http://www.edexcel.com/migrationdocu...2_US020961.pdf

"candidates, who correctly identified that
the water at Y was moving upwards"

**** edexcel.
So the mark scheme says vertically downwards, the examiners report says vertically upwards, and I still don't know how to get either of them
20. ..

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