AQA Physics: PHYA1 Tuesday 19th May 2015 (AM) and PHYA2 Thursday 04th June 2015 (PM)x

Original post by Questioner1234

Does the weak nuclear force affect all Hadrons or just protons and neutrons?

All hadrons (and leptons for that matter) are affected by the weak force.

Reply 381

Original post by Questioner1234

Does the weak nuclear force affect all Hadrons or just protons and neutrons?

Yes all hadrons
All baryon decay into proton through week interaction

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Reply 382

Questioner1234

7

Original post by C0balt

Yes all hadrons
All baryon decay into proton through week interaction

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Thanks. It's just that in the table in the official Aqa textbook on page 20 in pions and kaons it does not say weak force. Is this an error in the book?

Reply 383

TSR-addict

Guys, when drawing feynman diagrams, eg for proton electron collision, how do we know which side to draw the proton and electron on. And how do we know whether the 'wiggly' line for the boson slants up or down/ which side the arrow points?

im really confused

Reply 384

Original post by Questioner1234

Thanks. It's just that in the table in the official Aqa textbook on page 20 in pions and kaons it does not say weak force. Is this an error in the book?

If Kaon decay through week interaction strangeness is not conserved

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Reply 385

Original post by TSR-addict

Guys, when drawing feynman diagrams, eg for proton electron collision, how do we know which side to draw the proton and electron on. And how do we know whether the 'wiggly' line for the boson slants up or down/ which side the arrow points?

im really confused

Wiggly upwards from left to right
From bottom to top is the time flow so yeah
For the five diagrams we have to know baryon is always on the left

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Reply 386

TSR-addict

Original post by C0balt

Wiggly upwards from left to right
From bottom to top is the time flow so yeah
For the five diagrams we have to know baryon is always on the left

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so the boson arrow always points from left to right?
how do we know?

Reply 387

Slenderman

How do we know whay charge the gauge boson is. I just tend to guess and it's right lol

Reply 388

Original post by TSR-addict

so the boson arrow always points from left to right?
how do we know?

Boson carries charge etc from left to right
For example beta minus decay neutron becomes proton and emits W- to gain positive charge
W- then decays into electron and anti neutrino

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Reply 389

Anon_98

19

Original post by TomAyy

The website has some examples which may help

Oh okay!- Thanks. :smile:

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Reply 390

the_googly

7

I'm struggling on pair production and annihilation. where can I study deeper?

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Reply 391

Original post by TSR-addict

Guys, when drawing feynman diagrams, eg for proton electron collision, how do we know which side to draw the proton and electron on. And how do we know whether the 'wiggly' line for the boson slants up or down/ which side the arrow points?

im really confused

Proton electron collision
The electron is fired at the proton so the boson(W) will go from the electron towards the proton in a diagonal direction (imagine that they y-axis is time)
W- going right is the same as W+ going left (but in this case as the electron is fired at the protron a W- boson should be used
Always keep hadrons on one side and leptons on the other. So just always have the hadrons on the left and leptons on the right
If this is the case, the proton would be on the left and the electron would be on the right
The products are a neutron and a neutrino
As the neutrino is not negatively charged, the W- boson will travel towards the left which allows a neutron to be formed from the proton

Electron-capture
This is the opposite. Assume that the proton captures the electron. For this to occur the proton must go towards the electron. So the W boson will be heading towards the right (assuming that the proton is on the left and the electron is on the right)
The way i work out whether it's a W+ or a W- is by seeing if the charge must be relocated.
For a proton to become a neutron, the positive charge must be moved elsewhere? That's why there's a W+ boson

FYI (IMPORTANT)
For the Jan 13 Paper, Question 3ci, the mark scheme is actually messed up (on my screen anyway)
The mark scheme shows that the proton is on the right hand side and the electron is even further to the right (no where near the diagram)
I assumed that because the proton was close to the lines on the right that the proton was on the right and the electron was on the left however all the labels (other than W+) should be shifted towards the left

Paper:http://filestore.aqa.org.uk/subjects/AQA-PHYA1-QP-JAN13.PDF
Mark scheme: http://filestore.aqa.org.uk/subjects/AQA-PHYA1-W-MS-JAN13.PDF

(edited 8 years ago)

Reply 392

Amara123

Will definitely check it out. Thank you. 😀

Reply 393

Slenderman

How do you draw this circuit? q6 i think.

The thermistor is my problem, it talks about a water bath in the mark scheme. No idea why. Haven't learnt anything about that, I remember something from GCSE though which is like some kind of heating with thing in a beaker of water and something about ice.. can't remember -__- Someone mind explaining?

Reply 394

Original post by the_googly

I'm struggling on pair production and annihilation. where can I study deeper?

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Pair production- energy to mass. energy must be equal to or higher than the rest energy (Mev) of both the particle and anti-particle which are emitted - located on the second page of the formula sheet. Basically if an electron and a positron is emitted it would be 2x the MeV of the 0.51.... Also remember that the rest mass energy is in MeV, so 1MeV is one million eV. You also have to know that the antiparticle (positron in this case) only lasts a fraction of a second as it is annihilated almost immediately. When the particle and anti-particle pair are produced, they curl away from each other as they have an opposite charge
There's something about how they are produced e.g. when a photon passes near a nucleus - hopefully someone can explain that in more detail

Annihilation- mass to energy. Forms 2+ (gamma ray) photons. Same situation with the energy produced.

Reply 395

Amara123

Original post by Slenderman

How do you draw this circuit? q6 i think.

The thermistor is my problem, it talks about a water bath in the mark scheme. No idea why. Haven't learnt anything about that, I remember something from GCSE though which is like some kind of heating with thing in a beaker of water and something about ice.. can't remember -__- Someone mind explaining?

We basically use a water bath and ice to change the temperature. Because as you increase the temperature of the thermistor the resistance decreases, and if you decrease the thermistor's temperature, the resistance increases. We do this by adding ice/a water bath to vary the temperature so we can measure current and voltage to work out the resistance (V=IR) and to see if this is true.
Hope that made scence.

Reply 396

jasminekatie

1

I’m really confused with this equation:

deltaE = hf = E_{1 -}E₂(where E1 is energy of the starting level; E₂ is the energy of the end level)

If the levels are negative, then surely if an electron drops down an energy level, the change in energy would be positive (eg. -5eV - (-10eV) = 5eV)...

but that doesn’t correspond with the theory of an electron emitting a photon with energy, where it would lose some energyAnyone understand my confusion?

Reply 397

Original post by Slenderman

How do you draw this circuit? q6 i think.

The thermistor is my problem, it talks about a water bath in the mark scheme. No idea why. Haven't learnt anything about that, I remember something from GCSE though which is like some kind of heating with thing in a beaker of water and something about ice.. can't remember -__- Someone mind explaining?

The water bath basically allows the temperature of the thermistor to be from around 0-100degreesC which wouldn't be possible otherwise
Ice is used to keep it cool
A bunsen burner is used to heat it up

Are you referring to question 7 June 2014?

Reply 398

Slenderman

Original post by Rik21

The water bath basically allows the temperature of the thermistor to be from around 0-100degreesC which wouldn't be possible otherwise
Ice is used to keep it cool
A bunsen burner is used to heat it up

Are you referring to question 7 June 2014?

**** forgot to quote the year, nah this is Jan 13.

Reply 399