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

1. (Original post by Plagioclase)
Okay very briefly:

"Explain why the resolution of optical light microscopes is limited by the wavelength of light" - because as you know, when a wave interacts with a feature that has a similar size to its wavelength, diffraction occurs. Mention the diffraction equation (i.e. when wavelength is similar to d, theta increases). When the diffraction angle is large, the light is scattered rather than being neatly reflected so you end up with noise and fuzziness.

"Why would using a single wavelength of light improve the quality of an image" - (this sort of came up in a section C a few years ago) The refractive index of a lens depends on the wavelength of light used (they mentioned this fact in the question though, you're not expected to know it) so different wavelengths of light are refracted by different degrees through the lenses, so you end up with different colours being focused by different amounts, leading to a poor image quality. Google chromatic aberration if you're interested.

"How a cathode works" - You've got the work function of the metal, which is basically the extra energy. You then use the boltzman factor with the temperature of the metal to calculate the proportion of electrons with enough energy for thermionic emission. Those electrons are then free to whizz off towards the sample.

"How secondary electrons are released when electrons hit the sample" - Basically the same as above but the extra energy is the energy needed for an atom in the sample to ionise and the thing supplying the energy is the accelerated electron colliding with and transferring energy to the atoms in the sample.
Which equation is the diffraction one? D=nsin(theta)?

Cheers

What's the work function?

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2. (Original post by Mutleybm1996)
Why

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If I had to guess, sometimes I don't read the articles, other times I just skim over it.
3. What's the work function???

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4. (Original post by Mutleybm1996)
What's the work function???

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The 'activation energy'
5. This exam was really nice last year

Expecting a horrible one today

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6. Good Luck everyone, we're probably going to need it!
7. good luck

8. I thought it was dsin(theta)

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9. (Original post by Tibbz2)
Good Luck everyone, we're probably going to need it!

I thought it was dsin(theta)

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10. Please tell me I wasn't the only person who found this exam disgustingly hard.
11. (Original post by kingofgames010)
Please tell me I wasn't the only person who found this exam disgustingly hard.
Me too! Though I was expecting that anyway :/ I didn't finish, left about 8 marks just completely blank
12. Thought that paper was good overall, some tricky parts. The only answer i can remember at the moment is 0.027m for the length of the plates, did anyone else get this?
13. (Original post by falconinni)
Thought that paper was good overall, some tricky parts. The only answer i can remember at the moment is 0.027m for the length of the plates, did anyone else get this?
Yh exactly that
14. (Original post by falconinni)
Thought that paper was good overall, some tricky parts. The only answer i can remember at the moment is 0.027m for the length of the plates, did anyone else get this?
Yeah I think so.

I also found it really hard. I couldn't answer the 4 marker on induction, or the two 1 markers beforehand (I know the answers now, not sure why but I just blanked out during the exam).

So yeah pretty damn difficult exam. Fortunately a lot of the section C questions were exactly has predicted! So I liked section C and the iodine-131 question, the result was utter ****...

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15. I messed up the 4 marker on induction and the 4 marker on this distance of the x plate Pretty hard exam tbh...
16. I found that okay.....ish.....

Didn't notice it was a nuclear decay -.- dammit
17. How was the cubic cm electron question solved?
18. (Original post by STATER)
How was the cubic cm electrons question solved?
Which other questions were on that page?
I can't remember that question......
19. (Original post by STATER)
How was the cubic cm electron question solved?
You used pV=NkT, rearranging for N/V. You then had to convert cm^3 to m^3
20. (Original post by Mutleybm1996)
Which other questions were on that page?
I can't remember that question......
It was in section C. You were asked to work out electron rate given a current and activation energy. Then they gave a pressure.

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