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    Don't judge me, I know it's a simple question for people who are good but:

    How do you know what something decays into when you don't know anything except the first part. E.g. On June 2011 PHYA1, a question was:

    Complete this equation for the decay of a K- meson

    K- -------> ........ + ......... + .........

    Also, how do you know what type of interaction something is undergoing and why. I think the above is weak but I'm not really sure If it is can you please please tell me why, thanks
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    I think its just something you have to know. Or of course if you know the exchange particle you may be able to deduce the products.by thinking of conservation laws and what interacts with what. But even then I still you think you need to have so idea of the decay
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    anyone else?
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    anyone???
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    (Original post by 3607)
    Don't judge me, I know it's a simple question for people who are good but:

    How do you know what something decays into when you don't know anything except the first part. E.g. On June 2011 PHYA1, a question was:

    Complete this equation for the decay of a K- meson

    K- -------> ........ + ......... + .........

    Also, how do you know what type of interaction something is undergoing and why. I think the above is weak but I'm not really sure If it is can you please please tell me why, thanks
    Look at the previous questions on the paper, they should give you some hints about how to do it.
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    (Original post by 3607)
    Don't judge me, I know it's a simple question for people who are good but:

    How do you know what something decays into when you don't know anything except the first part. E.g. On June 2011 PHYA1, a question was:

    Complete this equation for the decay of a K- meson

    K- -------> ........ + ......... + .........

    Also, how do you know what type of interaction something is undergoing and why. I think the above is weak but I'm not really sure If it is can you please please tell me why, thanks
    pion, electron, anti-electron-neutrino.

    I know that happens because I know that pions have a smaller mass and are more stable than kaons.
    It wants thee paricles so I assume the other two are an electron/positron and an anti-neutrino/neutrino. The negative charge is conserved by the electron so I use that combo.

    Don't you have that exam on monday? Good luck!
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    (Original post by Occams Chainsaw)
    pion, electron, anti-electron-neutrino.

    I know that happens because I know that pions have a smaller mass and are more stable than kaons.
    It wants thee paricles so I assume the other two are an electron/positron and an anti-neutrino/neutrino. The negative charge is conserved by the electron so I use that combo.

    Don't you have that exam on monday? Good luck!
    Very good, though in fact it cannot just be a pion that it decays into as the velocity of the centre of mass is not allowed to change and if only a pion was emitted it would have to have more enregy and therefore the velocity of the centre of mass would change. Just in case you are interested
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    (Original post by Occams Chainsaw)
    pion, electron, anti-electron-neutrino.

    I know that happens because I know that pions have a smaller mass and are more stable than kaons.
    It wants thee paricles so I assume the other two are an electron/positron and an anti-neutrino/neutrino. The negative charge is conserved by the electron so I use that combo.

    Don't you have that exam on monday? Good luck!
    Thanks

    Yeah I do, I'll need all the luck I can get!
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    (Original post by natninja)
    Very good, though in fact it cannot just be a pion that it decays into as the velocity of the centre of mass is not allowed to change and if only a pion was emitted it would have to have more enregy and therefore the velocity of the centre of mass would change. Just in case you are interested
    What about if it happened so close to a nucleus that momentum could be conserved?

    Just curious!

    EDIT: I assume that when you talk about velocity it's actually the momentum you need to conserve. Excuse my ignorance!
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    (Original post by Occams Chainsaw)
    What about if it happened so close to a nucleus that momentum could be conserved?

    Just curious!

    EDIT: I assume that when you talk about velocity it's actually the momentum you need to conserve. Excuse my ignorance!
    yes then it could decay to just a pion but a photon would also be emitted coupling the nucleus into the system and no I'm not talking about momentum as we're now in the realms of special relativity, 3-momentum is not conserved, but 4-momentum, but as a consequence of conservation of momentum the COM must move with a constant velocity or the momentum of the zero momentum frame changes and that isn't allowed unless there are external forces
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    (Original post by natninja)
    yes then it could decay to just a pion but a photon would also be emitted coupling the nucleus into the system
    oh. that kind of complicates things lol.

    Thanks It's all pretty interesting but the A level spec. doesn't really say much about quarks which sucks! I'm hoping we go into it in a lot more detail in the A2 year!
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    (Original post by natninja)
    yes then it could decay to just a pion but a photon would also be emitted coupling the nucleus into the system and no I'm not talking about momentum as we're now in the realms of special relativity, 3-momentum is not conserved, but 4-momentum, but as a consequence of conservation of momentum the COM must move with a constant velocity or the momentum of the zero momentum frame changes and that isn't allowed unless there are external forces
    I have no idea what is going on in the system you just described. I'll try to work it out and get back to you! Thanks though!
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    (Original post by Occams Chainsaw)
    I have no idea what is going on in the system you just described. I'll try to work it out and get back to you! Thanks though!
    learn about minkowski space and 4-vectors and tensors
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    (Original post by 3607)
    Don't judge me, I know it's a simple question for people who are good but:

    How do you know what something decays into when you don't know anything except the first part. E.g. On June 2011 PHYA1, a question was:

    Complete this equation for the decay of a K- meson

    K- -------> ........ + ......... + .........

    Also, how do you know what type of interaction something is undergoing and why. I think the above is weak but I'm not really sure If it is can you please please tell me why, thanks
    That isn't in june 2011
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    (Original post by Qari)
    That isn't in june 2011
    I think you might want to read the second line of his post again.
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    (Original post by Occams Chainsaw)
    I think you might want to read the second line of his post again.
    It says
    e.g. On June 2011 PHYA1, a question was:

    Complete this equation for the decay of a K- meson

    K- -------> ........ + ......... + .........

    also they wouldn't give a question like this without some information because you can have anything in their that will work
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    (Original post by Qari)
    It says
    e.g. On June 2011 PHYA1, a question was:

    Complete this equation for the decay of a K- meson

    K- -------> ........ + ......... + .........

    also they wouldn't give a question like this without some information because you can have anything in their that will work
    Wrong. Only 2 variations will work

    K- →π0 + e- + (anti)v(e)
    OR K− →π 0 + µ− + (anti)v(µ)

    Anything else and stuff would not be conserved.
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    (Original post by Occams Chainsaw)
    oh. that kind of complicates things lol.

    Thanks It's all pretty interesting but the A level spec. doesn't really say much about quarks which sucks! I'm hoping we go into it in a lot more detail in the A2 year!
    Sorry to disappoint, but you don't talk about quarks again at A2 xD You do learn other mindbending stuff though
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    (Original post by YThursday)
    Sorry to disappoint, but you don't talk about quarks again at A2 xD You do learn other mindbending stuff though
    That sucks. I'll have to wait to see what it is. Charge is very interesting!
    The stuff on electric and magnetic fields looks good! as does stuff on capacitance. Apart from that I think everything else on the AQA spec seems pretty intuitive/obvious and won't be that enlightening. Maybe I'm wrong though!
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    (Original post by Occams Chainsaw)
    That sucks. I'll have to wait to see what it is. Charge is very interesting!
    The stuff on electric and magnetic fields looks good! as does stuff on capacitance. Apart from that I think everything else on the AQA spec seems pretty intuitive/obvious and won't be that enlightening. Maybe I'm wrong though!
    I'm not a huge fan of charge and capacitance. I like gravitational, electric and magnetic fields though The nuclear side is awesome too. Don't get me started on simple harmonic motion
 
 
 
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