AQA confusing Exam questions HELP! - particle physics

me - again!

I just cant get my head round some things - I just dont understand them!
My physics teacher is so bad in explaining and half the time he is not in lesson anyway!
So I REALLY need your HELP guys!

My little list:

June 2006

http://www.aqa.org.uk/qual/gceasa/qp-ms/AQA-PA01-W-QP-JUN06.PDF

5b)

(i) How do I know how many wavelengths are emitted?
How do I interpret the images?

(ii) No idea what so ever! :confused:

6b)
no idea where I can get that equation from.
Honestly, no idea, not done in lesson, not in revision guide.

January 2005

http://www.aqa.org.uk/qual/gceasa/qp-ms/AQA-PA01-W-QP-JAN05.PDF

3b)

(iii) A sigma plus particle is a baryon - Which baryon will the sigma plus eventually decay into?
we havent done this in lesson, and there isnt anything about this in my revision guide!
How does it decay and How do I know that a proton comes out?
Can you calculate it?

General Questions

My biggest problem, is that I really dont understand Exchange Particles (weak interaction)

For example:

1. p-> v + ve + e+
How do I know that the proton decays exactly in THAT way, and why?

2. n + ve -> p + e-
How do I know that the 1st part is converted into the second part?

and what is Beta decay and how does it work?

Honestly, I havent got a single clue how I can pass that Exam 2morrow!
Pleas people, I need your Help!

Kerstin (Kathrins sis) xx

Reply 1

F1 fanatic

16

please can you post actual questions since just saying "June 2006" doesn't help us much if we don't have the papers.

Reply 2

F1 fanatic

16

Oh, as for beta decay, basically its the conversion of a neutron into a proton (or vice versa in the case of beta plus decay) through the weak interaction, emitting an electon/positron and an anti-neutrino/neutrino. As for how you know, to an extent you have to remember it, but you can check it's right by knowing that you have to conserve charge, baryon number and lepton number.

Reply 3

Kathrin

OP

7

F1 fanatic

Oh, as for beta decay, basically its the conversion of a neutron into a proton (or vice versa in the case of beta plus decay) through the weak interaction, emitting an electon/positron and an anti-neutrino/neutrino. As for how you know, to an extent you have to remember it, but you can check it's right by knowing that you have to conserve charge, baryon number and lepton number.

Thanks - that makes more sense now.
But what is a lepton number.
I thought I only need to know charge, strangeness and baryon number...
I know what leptons are, but lepton number?

Reply 4

F1 fanatic

16

Kathrin

Thanks - that makes more sense now.
But what is a lepton number.
I thought I only need to know charge, strangeness and baryon number...
I know what leptons are, but lepton number?

it's the same principle as baryon number, except that it applies separately to electrons, muons and tau. so the leptons (e- and ve) have lepton number +1 and the anti-leptons (e+ and vebar) have lepton number -1.

as for your questions, 3b doesn't seem to correspond since in that paper Q3 is a question on reflection.

5a) i) every line must join to every other line from the 4th level to the 1st level.

namely, 1-4, 1-3, 1-2, 2-3, 2-4, 3-4 ie 6 lines.

ii) longest wavelength corresponds to shortest energy, since E=hf=hc/lambda.
In other words, it's the photon emitted for a transition between the 2 levels which are closest together in the energy level diagram.

6b) Well this is like the question you asked, except at the quark level. so you need to know that

proton = uud
neutron = udd
where u=up quark, and d=down quark.

Therefore, in beta- which is a neutron decaying to a proton, it's actually a down quark decaying to an up quark. Therefore:

d \rightarrow u + e^- + \bar{\nu_e}

Nice to see the old AQA papers again. I did AQA back in the day. Doesn't look like it's changed. I still have that data sheet on my wall!

Reply 5

Kathrin

OP

7

F1 fanatic

it's the same principle as baryon number, except that it applies separately to electrons, muons and tau. so the leptons (e- and ve) have lepton number +1 and the anti-leptons (e+ and vebar) have lepton number -1.

as for your questions, 3b doesn't seem to correspond since in that paper Q3 is a question on reflection.

5a) i) every line must join to every other line from the 4th level to the 1st level.

namely, 1-4, 1-3, 1-2, 2-3, 2-4, 3-4 ie 6 lines.

ii) longest wavelength corresponds to shortest energy, since E=hf=hc/lambda.
In other words, it's the photon emitted for a transition between the 2 levels which are closest together in the energy level diagram.

6b) Well this is like the question you asked, except at the quark level. so you need to know that

proton = uud
neutron = udd
where u=up quark, and d=down quark.

Therefore, in beta- which is a neutron decaying to a proton, it's actually a down quark decaying to an up quark. Therefore:

d \rightarrow u + e^- + \bar{\nu_e}

Nice to see the old AQA papers again. I did AQA back in the day. Doesn't look like it's changed. I still have that data sheet on my wall!

yep! I get it!

may I call you physics god :biggrin:

I edited Question 3 - it was a January '05 paper.

I'll come back to you when I get stuck again :smile:

Reply 6

Kathrin

OP

7

ehm,... what are fundamental particles?

Reply 7

F1 fanatic

16

3b) iii) ok so first let's work out the quark configuration. It's a baryon with a strange, the rest is u and d... that means to conserve charge we'll need it to be uus

now, given it has a strange quark in it, it has to decay weakly (as far as you're concerned) which means that the strange must go from an s to a u so that would give us a uuu. which if I recall correctly is a

\Delta^{++}

.

However, it says what does it finally decay to, and I would then argue that it decays to a proton, since a proton is the only stable baryon. In short I'm not too convinced by this question, I suspect I'm making it harder than it needs to be.

as for fundamental particles - these are particles which can't be broken down any further, they are not made up of other things. An atom is not fundamental since it is made of protons, neutrons and electrons. Neutrons aren't either because they are made of quarks. However, quarks and electrons etc are fundamental because they are not believed to be made up of anything else.

Reply 8

Lucien_Roach

10

Kathrin

ehm,... what are fundamental particles?

the smallest particles we know of... quarks and leptons

quarks make up sub-atomic particles such as protons and neutrons, as well as other particles

and Leptons (electrons, tau, Mu and their associated neutrinos)

AQA confusing Exam questions HELP! - particle physics

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