Exam Discussion!

[chuck981996]

Hey what did everyone say for the Diffraction patterning of the Electrons and the X rays?

I said:

• For the diffraction patterns to be the same, the electron must have a de Broglie wavelength equal to the wavelength of the photon.
• Since , the de Broglie wavelength is dependent on both the mass and the energy of the electron.
• Therefore, even though their energies are the same, the photon and electron have a different mass and thus have a different wavelength and different diffraction patterns.

[floyd.everest]

I said:

• For the diffraction patterns to be the same, the electron must have a de Broglie wavelength equal to the wavelength of the photon.
• Since , the de Broglie wavelength is dependent on both the mass and the energy of the electron.
• Therefore, even though their energies are the same, the photon and electron have a different mass and thus have a different wavelength and different diffraction patterns.

Hey wouldn't you be incorrect just in implying the photon has mass?

[chuck981996]

Yeah I had the same jist with the De Broglie wavelength! I did rearrange the equation with the Square root of 2mE to just mv, just to simplify things

Oh yeah, I just used that form of the equation (I had like 5 on my cheat sheet lel) because it shows clearly that wavelength is dependent on more than just energy. That sort of becomes lost when you use the standard lambda=h/p

[chuck981996]

Hey wouldn't you be incorrect just in implying the photon has mass?

Hm I don't know. Do you think I was implying that? It depends how mean the examiners are I guess. The important point was the an electron has mass, so it's momentum and energy aren't directly proportional, unlike for a photon. Perhaps that would have been a better way to word it.

[Stew_822]

Does anyone remember what they got for the height of the projectile in the second question? I think I got like 3.75 but then I tried it again two different ways and ended up with like three different answers and then I tried working backwards from my original answer to see if it was right and like I'm pretty sure it's not because I ended up with a totally different time than what I used to calculate the 3.75.....

[chuck981996]

Does anyone remember what they got for the height of the projectile in the second question? I think I got like 3.75 but then I tried it again two different ways and ended up with like three different answers and then I tried working backwards from my original answer to see if it was right and like I'm pretty sure it's not because I ended up with a totally different time than what I used to calculate the 3.75.....

What was the distance to the screen?

[Stew_822]

Pretty sure it was 26 meters, but we had to find the height that the projectile hit a board. I think it had an initial velocity of 20m/s at an angle of 30 degrees from the ground. Never done a question like this before so not sure if I had the right method

[TheFlyingWeed]

Does anyone remember what they got for the height of the projectile in the second question? I think I got like 3.75 but then I tried it again two different ways and ended up with like three different answers and then I tried working backwards from my original answer to see if it was right and like I'm pretty sure it's not because I ended up with a totally different time than what I used to calculate the 3.75.....

I'm pretty sure I had 3.75 as well

[Stew_822]

I'm pretty sure I had 3.75 as well

Cool! Maybe I got it right then!

[FSH7]

Who did the sound detailed study? I got A C C D D C B C B A B.

[chuck981996]

Pretty sure it was 26 meters, but we had to find the height that the projectile hit a board. I think it had an initial velocity of 20m/s at an angle of 30 degrees from the ground. Never done a question like this before so not sure if I had the right method

If it was 26m, the formula I used yields 3.75m too:

http://www.wolframalpha.com/input/?i=26*tan%2830%C2%BA%29-%2810*26%5E2%29%2F%282*%2820*cos%2830%C2%BA%29%29%5E2

[isuru.e]

Who did the sound detailed study? I got A C C D D C B C B A B.

Got them except for 8 and 11. Im probably wrong though.

[FSH7]

Got them except for 8 and 11. Im probably wrong though.

I'm not quite sure about question 8 or 11 either to be honest. I thought that the person would hear the low frequency instruments for longer because of greater diffraction.

[swaggydawg]

Did anyone else find special relativity hard this year or was that just me?

[jumcakes]

Although I don't think it will be too much of a hassle, I believe if you used exact/non truncated values the projectile question turned out to be 3.74 metres (3.744something).

Which question was Question 8, if you can remember?