AQA Physics Unit 1 PHYA1 20th May 2013

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

Please help! I want full ums!

1 MeV is = to 1.6x10^13 HOWEVER! 1eV is 1.6x10^-19

Reply 821

WordPad

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

Please help! I want full ums!

eV = J / 1.6^-19
mev = j/1.6^-13 because m = million therefore -6 from 19 gives you 13

Reply 822

x-Sophie-x

13

Does a variable resistor vary the current initially? Or resistance? Or both?

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Reply 823

Sukura

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.

:smile:

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Oh thank you so much!! I was so confused for the longest time I appreciate it :smile:

I'm so silly but thank you!!! Best of luck to all of you on the exam! We will all get straight As!,

Reply 824

username1099191

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. :smile:

Reply 825

Ephixa

Electricity help pls any good websites

Reply 826

posthumus

20

Could anyone please run me through examples of strong interactions? :smile:

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

seems like electrostatic interaction :s-smilie:

But anyways, are there any more examples some of you guys can share ? :smile:

Thanks in advance

Reply 827

x-Sophie-x

13

Original post by Sukura

Oh thank you so much!! I was so confused for the longest time I appreciate it :smile:

I'm so silly but thank you!!! Best of luck to all of you on the exam! We will all get straight As!,

Haha your welcome :smile:

I made that mistake too at first!

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Reply 828

Surf

15

Well, see ya guys, good luck.... I've got to leave now...
Remember to relax - take it one question at a time!
:cool:

Reply 829

Cheesegrater4

7

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. ??

Reply 830

NtainS

What time is the exam again? :s-smilie:

Reply 831

IWantSomeMushu

17

To convert from mA to A do you simply multiply by 10^-3?

Reply 832

Substitution

3

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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

Reply 833

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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Reply 834

x-Sophie-x

13

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. :smile:

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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Reply 835

NtainS

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.

Reply 836

x-Sophie-x

13

Original post by IWantSomeMushu

To convert from mA to A do you simply multiply by 10^-3?

Yup

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Reply 837

sceezy

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)

Reply 838

usycool1

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) :smile:

(edited 10 years ago)

Reply 839

x-Sophie-x

13

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?

Posted from TSR Mobile

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 :smile:

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AQA Physics Unit 1 PHYA1 20th May 2013

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