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# The Physics PHYA2 thread! 5th June 2013 watch

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1. (Original post by .raiden.)
90 and 270
Or
Pi/2 and 3pi/2
I put 1/4lambda and 3/4 lambda, will that get the marks?
2. The question 7C .. all u had to say was because the seismic wave was polarised, it is a transverse wave, because longitudinal waves cant be polarised.
3. Hi guys. I wanted to know for 1c where you calculate the acceleration of the glider was I right in using the resultant force of approx 6100?

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4. (Original post by jonny7bell)
I put 1/4lambda and 3/4 lambda, will that get the marks?
Its usually given in degrees or radians but you might be lucky
5. (Original post by v.007)
Hi guys. I wanted to know for 1c where you calculate the acceleration of the glider was I right in using the resultant force of approx 6100?

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Yes you can use the rounded or calculated value, you won't lose marks
6. (Original post by masryboy94)
it asked for monochromatic not coherent
I put both answers down do I get penalized do you think?
7. (Original post by lebron_23)
PHYA2 (Provisional, and very shaky) Mark scheme;

Question 1 – Simple matter of working out forces and that stuff, efficiency question may cause problems though.

1) 6082N, which is 6100 to 2sf (2)
b) 9.5 degrees using arctan of 1000/6000 (2)
c) Acceleration was 9.2ms^-2 (2)
d) Can’t remember what this one was asking but I got 3.9x10^6 (not sure) (2)
e) I got 20.5% but I’m not sure as I’ve heard people give various answers (3)

Question 2 – Fairly straightforward question about projectiles.

2) Time taken was 0.55s (2)
b) The horizontal distance was 248m I think (2)
c) As both bullets have the same mass, S=ut will be smaller for the bullet with the lower horizontal velocity (3?) An addition as suggested by ThomT94; 'Also, bullet b's distance is not affected by its mass. It's because both accelerate towards the ground at the same rate from the same height, therefore, same time of travel, thus lower horizontal speed causes bullet to travel shorter distance in the given time.'
-- Can’t remember if there was anything more to this question

Question 3 – Perhaps the best 6 marker they’ve ever given, very straightforward.

3) The ball begins to accelerate with a large acceleration as its weight force is (one of) the only forces acting as it begins to move. The gradient then begins to slowly decrease as the resistive forces begin to balance out the weight force. The ball finally reaches terminal velocity as the resistive forces balance out the weight force. Appropriate reference to Newton’s first law needed. Then the ball remains at that velocity, as there is no external force, give reference to Second Law. (6)
b) Initially a straight line indicating uniform acceleration, then a curve of decreasing gradient ending with the ball at terminal velocity. (3)

Question 4 – A decent question, I guess.

4) Weight of the ball was 0.44N (2sf) using volume of a sphere which is given in the data sheet!!! (4)
b)Hooke’s law states that force applied is proportional to the extension up to the limit of proportionality (2)
c) Gradient was roughly 1150/1100 Nm^-1needed (3)
d) Using the area of a triangle and then counting (roughly) 9 small boxes each of area 0.025 gave 1.08J (3?)
e) Straight line parallel to the first one but not finishing at zero as plastic deformation has occurred (2)
f) Plastic deformation means the object won’t return to its original shape/length once the load is removed (1)
g) Work is less as area under graph is less energy absorbed as heat and in permanent extension (1)

Question 5 – Wasn’t too bad..

5) Two conditions for TIR were an angle greater than the critical angle and moving from a medium of higher refractive index to lower (2)
b) Defining the frequency of a progressive wave. Just explain the equation? (1)
c) Speed of light in the object thing was 1.7x10^8 (2)
d) Proof that the angle was about 31.8 degrees using Snell’s Law
e) Critical angle was 51.1 degrees using 1/sinc (2)
f) Undergoes TIR as (20+31.9) > 51 (2)

Question 6 – Don’t even know, seemed cool..

6) First phase difference was 90 degrees or pi/2. Second was 270 degrees or 3pi/2 (2)
b) Oscillation between maximum and minimum amplitude; i.e moves up and down (2)
c) Polarisation only occurs in transverse waves; mention something about plane of polarisation (2)
d) Define frequency (1)
e) 750m (2)

Question 7 – I may have flopped

7) All of the light has the same wavelength (1)
b) Can’t really remember – According to Frogs491 its ‘Fringes larger so intensity equal’ -- If this is the graph of intensity, then (2)
c) Safety precautions that need to be taken when dealing with laser light can include; wearing reflective glasses; taking care not to shine the light in your eyes (or other people's eyes for that matter); any other sensible answer (2)
e) Last part; white at central maxima and very bright as all of the wavelengths converge at the centre; blue tinge closer to central maxima and red tinge further away; not sure about anything else. (3)

That’s all I can remember guys. I’ve probably omitted quite a few things so if anyone can spot any mistakes, let me know and I’ll make amendments

EDIT: I'm going to start adding in the marks for each question slowly so that should be half done soon. If anyone can remember what the marks are for each question please let me know! Thanks. Done

Got the majority of it now, seems we're one mark over though, so if anyone can spot where the marking is wrong.. Mucho gracias

Still missing some stuff over here guys. Although this post is likely long forgotten now..
I'm pretty sure 6c was only one mark
8. (Original post by Hullo)
I put both answers down do I get penalized do you think?
As long as your points don't contradict they will just ignore the not needed points
9. (Original post by .raiden.)
Its usually given in degrees or radians but you might be lucky
Surely as you weren't given the actual wavelength and the values of A,B and C. It would make more sense to put the wave in terms of lambda. That was my reasoning anyway, I would find it a little harsh to lose marks because of it.
10. (Original post by Abbseh)
I'm pretty sure 6c was only one mark
It was 2, we managed to find which question wasn't an extra mark
11. (Original post by .raiden.)
Yes you can use the rounded or calculated value, you won't lose marks
Thanks dude! How did you draw the graph for the steel ball in oil. I drew straight line up to the first dotted line. The drew a curve sloping downwards and flattening out at terminal velocity from there on...?

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12. (Original post by Abbseh)
I'm pretty sure 6c was only one mark
No I remember it being 2.
13. (Original post by HenryD)
Fairly sure that that question was about monochromatic light? In which case same wavelength is the answer.
Hi henry i need your help!!!! for q2c i put s=0.5(u+v)t and as u is higher s is going to be higher, and i explained it, will i get any marks?
also, Q5a for the condition i wrote the critical angle, but i wrote that the refrative index of both of them divided has to be higher than 1, if that makes sense?
lastely! Q6a i wrote 1/4(lambda) in phase and 3/2(lambda) out of phase would i get any marks? surely one right ?? thanks in advance!!
14. Got 247m for the horizontal distance and no working because of time, do I still get both marks?
15. (Original post by v.007)
Thanks dude! How did you draw the graph for the steel ball in oil. I drew straight line up to the first dotted line. The drew a curve sloping downwards and flattening out at terminal velocity from there on...?

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This is what I did, it was probably wrong lol
Attached Images

16. (Original post by gandanmo)
Q6a i wrote 1/4(lambda) in phase and 3/2(lambda) out of phase would i get any marks? surely one right ?? thanks in advance!!
Exactly what I did, and considering they didn't actually give you the wavelength, I would be pissed off if I lost the marks.
17. (Original post by trentjoseph007)
The question 7C .. all u had to say was because the seismic wave was polarised, it is a transverse wave, because longitudinal waves cant be polarised.
It told you the wave was transverse, you had to say it was a seismic s wave
18. (Original post by trentjoseph007)
Attachment 223636

Look at figure 2 ... Thats what happens .. Not white central fringe .. or first order continuous spectra.

EDIT: This is the last question on the paper.
That one is for red monochromatic light

^ that is what happens.
19. (Original post by Davelittle)
It told you the wave was transverse, you had to say it was a seismic s wave
it was other way round mate.
20. (Original post by gandanmo)
Hi henry i need your help!!!! for q2c i put s=0.5(u+v)t and as u is higher s is going to be higher, and i explained it, will i get any marks?
also, Q5a for the condition i wrote the critical angle, but i wrote that the refrative index of both of them divided has to be higher than 1, if that makes sense?
lastely! Q6a i wrote 1/4(lambda) in phase and 3/2(lambda) out of phase would i get any marks? surely one right ?? thanks in advance!!
Hello, hmm:
2C) You'll get marks for that yes, you may even get full marks if you explained why t will be the same? If not then 1 or 2 marks (probably 2 if you explained).
5A) Depending on how you wrote it you may get the mark for that, sounds a little ambigious but if the examiner understands you you'll get the mark. 1-2/2
6A) Someone else on here did the same, it's possible that they'll give you that if they're lenient. Probably a 50 50 toss up between whether you get the marks or not.

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