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# OCR PHYSICS B G495~ 18th June 2015 AM ~ A2 Physics watch

1. (Original post by urz13)
How on earth do you calculate the emf from the gradient of the graph in Q11 part b) here?

(June 2014 paper)

Thanks!
Draw a tangent on the curve at the point where the gradient is steepest.
2. (Original post by Iridann)
Those are their charges I'm talking about spin values. https://en.wikipedia.org/?title=Quark#Spin

Turns out quarks do have half spin values.
Oh ffs, sorry, I can't read today

Really hope I sleep well tonight or else I'm ****ed.
3. (Original post by urz13)
How on earth do you calculate the emf from the gradient of the graph in Q11 part b) here?

(June 2014 paper)

Thanks!
Nevermind - I missed the fact that time was in ms.
4. (Original post by STATER)
Does the Pauli exclusion principle mean that there can only be one electron at each energy level at any given time?
It does indeed, yes
5. (Original post by h4mz4)
How do u work out wavelength of electron if u have h-6.6*10^-34 m- 9.1*10^-31 and also KE 2*10^-18

Thanks
use K.E=1/2*m*v^2 and wavelength = h/p = h/mv to work out wavelength as = 0.35nm
6. (Original post by smerkz)
It does indeed, yes
One last question. In line 56 of the pre release, it says that xrays are produced. It's because the incoming electron transfers energy to the stationary electron which then rises to a higher energy level. But what causes it to fall back down to emit the X ray?
7. (Original post by urz13)
How on earth do you calculate the emf from the gradient of the graph in Q11 part b) here?

(June 2014 paper)

Thanks!
Do you have a mark scheme for june 2014??
8. (Original post by Iridann)
use 1/2 * mv^2 = hc/lambda
Isn't that what I said?

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9. (Original post by HennersPD)
use K.E=1/2*m*v^2 and wavelength = h/p = h/mv to work out wavelength as = 0.35nm
Why can't you use E=hc/lamda?

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10. (Original post by Mutleybm1996)
Why can't you use E=hc/lamda?

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thats the same just written differently haha! either way works just fine! how're you feeling for this, did you find g494 good?
11. (Original post by HennersPD)
thats the same just written differently haha! either way works just fine! how're you feeling for this, did you find g494 good?
Weird
I get 9.9x10^-8
When I use E=hc/lambda

Assuming E is 2x10^-18

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12. (Original post by HennersPD)
thats the same just written differently haha! either way works just fine! how're you feeling for this, did you find g494 good?
Not sure how many marks I lost
Quite a few on silly mistakes
Hopefully I got an A
I just need an A in this to be safe

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13. I thought you could have two electrons at any energy level at a time... But a maximum of two
14. (Original post by francescafisher)
I thought you could have two electrons at any energy level at a time... But a maximum of two
I think thats only the case in the first energy level and its something to do with spin that we don't need to know.
15. Can anyone help me with re-arranging the relativistic factor equation to find velocity when you have the relativistic factor?
I'm wracking my brains to do it but I just can't get the right answer.
16. (Original post by Tibbz2)
Do you have a mark scheme for june 2014??
Here you are (hopefully this link works, if not theres a link to all past papers and markschemes on P1 or 2 of this thread)
17. (Original post by urz13)
Here you are (hopefully this link works, if not theres a link to all past papers and markschemes on P1 or 2 of this thread)
That would be the local directory :P
18. can anyone tell me everything I need to know about bosons please? Read this https://en.wikibooks.org/wiki/A-leve...hysics)/Bosons it didn't help. In particular I don't get the weak nuclear force, thanks
19. (Original post by G_Parv)
Can anyone help me with re-arranging the relativistic factor equation to find velocity when you have the relativistic factor?
I'm wracking my brains to do it but I just can't get the right answer.
Steps
Square both sides
Multiply by (1-v^2/c^2)
Divide by gamma^2
Take the v^2/c^2 the other side
Times by c^2
Square root everything

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Really worried

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