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# AQA Physics Unit 1 PHYA1 20th May 2013 watch

1. (Original post by Sukura)
When you convert MeV into joules, how do you know what to multiply it by? One past paper says 1.6x10-13 and another said 1.6x10-19

The past paper is: jan 2011 question 3

1 MeV is = to 1.6x10^13 HOWEVER! 1eV is 1.6x10^-19
2. (Original post by Sukura)
When you convert MeV into joules, how do you know what to multiply it by? One past paper says 1.6x10-13 and another said 1.6x10-19

The past paper is: jan 2011 question 3

eV = J / 1.6^-19
mev = j/1.6^-13 because m = million therefore -6 from 19 gives you 13
3. Does a variable resistor vary the current initially? Or resistance? Or both?

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4. (Original post by x-Sophie-x)
To convert MeV to J use ten to the minus thirteen.

And to convert eV to J use ten to the minus nineteen.

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Oh thank you so much!! I was so confused for the longest time I appreciate it I'm so silly but thank you!!! Best of luck to all of you on the exam! We will all get straight As!,
5. (Original post by x-Sophie-x)
So why does the incident photon/electron have to give the atomic electron an exact amount of energy?

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Think of the atomic electron having to hop up a flight of stairs, with one stair representing one energy level. The atomic electron has to take an amount of energy equivalent to exactly one or two or three (or etc etc) stairs as it cannot stop halfway up a stair, and those amounts of energy depend on the atom (i.e. the element).

For example, if the difference between n=1 and n=2 is 10eV, both an electron with 11.2eV of Ek and an electron with 12.1eV of Ek will have to transfer that 10eV of energy for the atomic electron to get there.
6. Electricity help pls any good websites
7. Could anyone please run me through examples of strong interactions?

I've seen: p + n ---> p + n

seems like electrostatic interaction But anyways, are there any more examples some of you guys can share ?

8. (Original post by Sukura)
Oh thank you so much!! I was so confused for the longest time I appreciate it I'm so silly but thank you!!! Best of luck to all of you on the exam! We will all get straight As!,
I made that mistake too at first!

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9. Well, see ya guys, good luck.... I've got to leave now...
Remember to relax - take it one question at a time!
10. (Original post by x-Sophie-x)
Does a variable resistor vary the current initially? Or resistance? Or both?

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i thought it varies the resistance so changes voltage. ??
11. What time is the exam again?
12. To convert from mA to A do you simply multiply by 10^-3?
13. Posted from TSR Mobile

to convert ev to joules you do x1.6x10^-19, mega is x10^6 so they added 6 to the first power to get x10^-13
14. Guys can someone explain to me in Jun 12, Q7.a.ii, it's asked us to calculate the resistance, and the correct equation is: R=(8/0.067) it even backs this up in the mark scheme. The answer to that is 119.4, so 119 right? But in the mark scheme it has rounded up to 120. I don't get why they've done this and it's really annoying me because I'll lose marks this way. Can someone please explain when I'm supposed to round up all of a sudden?

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15. (Original post by jazzynutter)
Think of the atomic electron having to hop up a flight of stairs, with one stair representing one energy level. The atomic electron has to take an amount of energy equivalent to exactly one or two or three (or etc etc) stairs as it cannot stop halfway up a stair, and those amounts of energy depend on the atom (i.e. the element).

For example, if the difference between n=1 and n=2 is 10eV, both an electron with 11.2eV of Ek and an electron with 12.1eV of Ek will have to transfer that 10eV of energy for the atomic electron to get there.
Thank you, that was a good explanation.

I understand why for excitation, although one thing that still confuses me is that in ionisation the electron completely leaves the atom in one go, so doesn't need exact energy values incident on it.. and the 'extra' energy is the KE on the electron.

Or have I completely missed the point here?

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16. (Original post by Cheesegrater4)
i thought it varies the resistance so changes voltage. ??
Variable resistor increases/decreases resistance. If you increase its resistance, the pd across it increases - however, by I=V/R, Current must decrease.
17. Hey, can anyone help me answer this question:

Explain what is meant by the ground state of an atom and describe the process that is taking place in the atoms emitting photons. (6 marks)
18. (Original post by IWantSomeMushu)
To convert from mA to A do you simply multiply by 10^-3?
Yup

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19. (Original post by FrankB3)
Guys can someone explain to me in Jun 12, Q7.a.ii, it's asked us to calculate the resistance, and the correct equation is: R=(8/0.067) it even backs this up in the mark scheme. The answer to that is 119.4, so 119 right? But in the mark scheme it has rounded up to 120. I don't get why they've done this and it's really annoying me because I'll lose marks this way. Can someone please explain when I'm supposed to round up all of a sudden?

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You probably won't lose marks, but you should use exact values rather than rounded values in calculation (the current is actually 0.666666666666....A so you should have used this)
20. (Original post by FrankB3)
Guys can someone explain to me in Jun 12, Q7.a.ii, it's asked us to calculate the resistance, and the correct equation is: R=(8/0.067) it even backs this up in the mark scheme. The answer to that is 119.4, so 119 right? But in the mark scheme it has rounded up to 120. I don't get why they've done this and it's really annoying me because I'll lose marks this way. Can someone please explain when I'm supposed to round up all of a sudden?

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Did they use 2sf in the question?
That's why they would have rounded to 120.

But don't worry, unless they ask you for a certain number of Sig figs, you won't lose marks if you give your answer to something appropriate

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