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

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.

Why


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What's the work function???


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Good Luck everyone, we're probably going to need it!

Please tell me I wasn't the only person who found this exam disgustingly hard.

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?

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?

How was the cubic cm electrons question solved?

How was the cubic cm electron question solved?

Which other questions were on that page?
I can't remember that question......