OCR Physics tomorrow "Electrons and photons" Watch

liz17
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#81
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#81
oh gosh I dont exactly remeber, probs 2 max for the first one, and pos 3 for the next. i really cant rember thou
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DealerG
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#82
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:cool: scratch the B then, i accounted my marks and i got 45 with a range of -/+2 , but if the charge question is 5 marks all together then i got 50 within the same range...its made my day lol thanks. (I'm sure i got the charge one right, deltaQ = I x deltaT, and electons is charge/1.6x10^-19)

Anything lower than 75% is a re-sit for me...
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NavalChicken
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#83
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(Original post by liz17)
I wrote about photo electric effect. then for KE ranging I noticed that the wavelength given above was in the region of visible light

As visible light is split into a spectrum of colours with ranging wavelengths and therfore ranging frequencys, I used this information to relate to the ranging KE. Because if you have ranging frequency then this will cause electrons to be released with different KE.

That make sense? What you think?
Thats a good response. But I thought the KE would be different depending on where the election was situated in the metal, obviously the work function is the minimum energy required for one metal to be emitted. For surface metals they would have a higher KE because they need less enery to overcome the work function thus have more energy to transfer to kinetic. Electrons deeper in the metal have a greater work function and thus need to use more energy in escaping from the metal and so have lower KE.

Saying that, I didn't write that :confused: I dedicated about 1 line to KE, with no mention of variation, I guess I glossed over that part of the paper :mad:

I thought the paper went quite well, but looking on here I've realised a few marks I may have missed. The only question I had a problem with was the mangetism question. I spoke to a friend after the exam and he seemed to go along with the theory I've seen on here, that the current decreases due to an increase in resistance, so the total force decreases. I didn't think of it like that, I think the question caught me out. I answered the whole paper before coming back to this one and in the end gave a rushed answer

My answer seems quite silly now. I said something along the lines of, the circumference of the coil decreases by a half, so therefore the coils magnetic field is more concentrated and therefore stronger. This leads to an increase in the force experienced.

I think I've achieved an A, as I said I've noticed a few mistakes now (the example above is annoying me!) and a few areas where my answer may not have gone into enough detail (KE answer) but I hope I didn't make too many silly calculations.

Edit: Also for the question on showing the current in terms of E & R for only 1 mark, I got the correct answer but didn't simplify meaning I had E/2R/3, which would've simplified to 3E/2R, do you think I'll lose the mark?
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DealerG
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#84
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(Original post by NavalChicken)
Edit: Also for the question on showing the current in terms of E & R for only 1 mark, I got the correct answer but didn't simplify meaning I had E/2R/3, which would've simplified to 3E/2R, do you think I'll lose the mark?
Should be OK, i write 1.5E/R which is the same as many of the other different versions of writting it. If your for example, a mark from a B then i have no doubt that they'll give it without hesitation or maybe even before.
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equinox3o0o
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naval i wrote that aswell i said that electrons are ejected from within the metal not from the surface thus requiring more energy, btw what did u get for the last question, find the wavelength
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NavalChicken
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I can't remember my answer for that question, but I think I can remember my method.

After deducing the K.E from the previous question, I used the equation  \frac{1}{2}MV^2 = ... and rearranged it to find the Velocity.

I then put the velocity value into the De Broglie equation to come out with an answer for the wavelenth.

Edit: Is the answer to what happens to the force generally accepted as being a decrease due to an increase in the resistance in this thread? I hope to get above 90, but where I thought that was almost a certainty right after the exam, now I'm not so sure. I may have missed a mark for not simplifying far enough, for getting the force question wrong and for not being explicit enough in why the KE varys, I think I just mentioned that photoelectrons gain KE when they overcome the work function, with no mention of any being more deeply rooted... I'm worrying too much!
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equinox3o0o
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#87
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lol dont worry youll drop maybe around 4 marks altogether which makes 56/60 which is still an A
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equinox3o0o
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#88
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btw naval did you get something like 11.5 for the EMF question? the one with the resistors...
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liz17
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#89
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I did!! I got exact that!
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equinox3o0o
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#90
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lizz!! i hope ur talking to me
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liz17
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#91
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I am indeed talkin to you e-3000!
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equinox3o0o
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#92
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waheyy!!
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liz17
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#93
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so snap with that answer!
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NavalChicken
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#94
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Glad to say I did
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DealerG
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#95
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I didn't...(stands alone in corner)

do you think they'll give a mark for stating the formula

wavelength = H/MV ????

And also for correct working considering the candidate only forgot to double 1/2MV after square rooting it?
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liz17
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#96
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Yes most probably!
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