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    Here is a simplied picture of a linac


    hth
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    From BBC news:

    Types of Accelerators

    Linear Accelerators

    The linear accelerator is the simplest type of accelerator. Fundamentally it is a long line of coils (or drift tubes) which charged particles are accelerated through. However, there are two types of linear accelerator. One type of accelerator is the standing-wave linear accelerator; particles travel along a cylindrical vacuum tank through a series of drift tubes, separated by gaps. As the particles cross the gaps, electromagnetic waves, called standing waves, accelerate them. (Or, more simply put, as the particle passes through the drift tube, the current through it is swapped. If the current was kept it would pull the particle back towards the tube when it leaves. Changing the current repels the particle from the end of the tube.) The waves provide an electric field that speeds up the particles by acting on their electric charges.

    This type of accelerator can only manage to accelerate particles to 200 MeV. (Ah, if you don't know what this is you should try and find out.) Physicists mainly use them as a primary accelerator that feeds into a synchrotron. In industry and medicine they are used as powerful X-ray machines.

    The other type of linear accelerator is the travelling-wave linear accelerator. This speeds particles through a single long pipe by an electromagnetic wave that travels with the particle. This high-frequency wave is called a travelling wave. As long as the wave speed matches the particles' speed, the particles will continue to gain energy.

    This type of accelerator can accelerate particles to 30 GeV, this is the Stanford Linear Collider, the longest accelerator in the world at 3.2km. The SLC is used to smash electrons and positrons into each other at 50 GeV to create uncharged weak bosons (the particle for the nuclear weak force).
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    So what could be the quetions for synchrotron or cyclotron?
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    how they work
    advantages
    disadvantages
    use of f = πm/Be for a semicircular path
    comparisons to other accelerators
    possibly graphs

    i'll learn it all tomorow and flick through phy1-phy5 again. Can't wait till i get this damn exam at the way, it's the most stressful 1 by far imo.
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    (Original post by nas7232)
    From BBC news:

    Types of Accelerators

    Linear Accelerators

    The linear accelerator is the simplest type of accelerator. Fundamentally it is a long line of coils (or drift tubes) which charged particles are accelerated through. However, there are two types of linear accelerator. One type of accelerator is the standing-wave linear accelerator; particles travel along a cylindrical vacuum tank through a series of drift tubes, separated by gaps. As the particles cross the gaps, electromagnetic waves, called standing waves, accelerate them. (Or, more simply put, as the particle passes through the drift tube, the current through it is swapped. If the current was kept it would pull the particle back towards the tube when it leaves. Changing the current repels the particle from the end of the tube.) The waves provide an electric field that speeds up the particles by acting on their electric charges.

    This type of accelerator can only manage to accelerate particles to 200 MeV. (Ah, if you don't know what this is you should try and find out.) Physicists mainly use them as a primary accelerator that feeds into a synchrotron. In industry and medicine they are used as powerful X-ray machines.

    The other type of linear accelerator is the travelling-wave linear accelerator. This speeds particles through a single long pipe by an electromagnetic wave that travels with the particle. This high-frequency wave is called a travelling wave. As long as the wave speed matches the particles' speed, the particles will continue to gain energy.

    This type of accelerator can accelerate particles to 30 GeV, this is the Stanford Linear Collider, the longest accelerator in the world at 3.2km. The SLC is used to smash electrons and positrons into each other at 50 GeV to create uncharged weak bosons (the particle for the nuclear weak force).
    are the words in brackets your own additions? because that is the only place I can find the words alternating current...
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    Im starting to like PHY6. Im finding it easier to score highly than in than PHY4 and 5. Its very straight forward, without any trademark edexcel mindgames. So you either know the answer, or not.
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    (Original post by mik1w)
    are the words in brackets your own additions? because that is the only place I can find the words alternating current...
    nah, i didn't add anything. all i did was do a search in google for 2 secs and pasted that from bbc directly...
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    Okay, I accept that the evidence is quite overwhelming against me... but can you just assure me that I'm not going mad, because this seemend pretty obvious to me that with no circuit, there is no current.
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    No circuit no current? I'm certainly not in the position to correct anyone here lol but... isnt there something wrong with that statement?

    Think of an AC supply connected to a solenoid, you chuck a Magnet through the solenoid, emf is induced from lenz's law. No circuit, but there is current?
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    (Original post by LT0918)
    No circuit no current? I'm certainly not in the position to correct anyone here lol but... isnt there something wrong with that statement?

    Think of an AC supply connected to a solenoid, you chuck a Magnet through the solenoid, emf is induced from lenz's law. No circuit, but there is current?
    If the ends are connected to a datalogger then there is no current flow, only an alternating voltage. If the ends are connected up then there will be a current flow so it produces an alternating current
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    As for the charge on the plates I would say an alternating voltage but im not going to argue with the markscheme so i'll put AC.
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    (Original post by nas7232)
    how they work
    advantages
    disadvantages
    use of f = πm/Be for a semicircular path
    comparisons to other accelerators
    possibly graphs

    i'll learn it all tomorow and flick through phy1-phy5 again. Can't wait till i get this damn exam at the way, it's the most stressful 1 by far imo.
    not as stressful as my line up :rolleyes: got Physics synoptic on monday, P4 and P6 maths on tuesday, and M4 on thursday :eek: , and i need A's in the maths for uni, and A in physics for uni as well...aghhh...what is worse, both my firm and insurance want an A in further maths, so i'm screwed if i dont get it - so stressful man!

    Pk
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    (Original post by LT0918)
    No circuit no current? I'm certainly not in the position to correct anyone here lol but... isnt there something wrong with that statement?

    Think of an AC supply connected to a solenoid, you chuck a Magnet through the solenoid, emf is induced from lenz's law. No circuit, but there is current?
    maybe Im missing something cos everyone seems to think the exact opposite to me.. but as I understand it,

    current = rate of flow of charge
    therefore a requirement of a current is the movement of charge
    a requirement of a movement of charge is a circuit - a path for charge to follow!

    on the diagram above (http://www.s-cool.co.uk/a-/phy-/part...rtic-dia01.gif) I don't see any circuit! I don't see electrons jumping from A to B or from C to D... how can there be a current when the charge has nowhere to go? each electrode (A,B,C.etc.) is surrounded by air and is a dead end for charge...

    :confused: is there something Im missing.. lol
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    (Original post by mik1w)
    maybe Im missing something cos everyone seems to think the exact opposite to me.. but as I understand it,

    current = rate of flow of charge
    therefore a requirement of a current is the movement of charge
    a requirement of a movement of charge is a circuit - a path for charge to follow!

    on the diagram above (http://www.s-cool.co.uk/a-/phy-/part...rtic-dia01.gif) I don't see any circuit! I don't see electrons jumping from A to B or from C to D... how can there be a current when the charge has nowhere to go? each electrode (A,B,C.etc.) is surrounded by air and is a dead end for charge...

    :confused: is there something Im missing.. lol
    I agree with you but im not going to argue with the markscheme
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    (Original post by SinghFello)
    Im starting to like PHY6. Im finding it easier to score highly than in than PHY4 and 5. Its very straight forward, without any trademark edexcel mindgames. So you either know the answer, or not.
    exactly!!!

    for me it's more often not knowing the answer, but i still appreciate knowing what the question wants me to do

    the fact that i dont really need to do that well in this also makes it ok for me
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    (Original post by Economist)
    I agree with you but im not going to argue with the markscheme
    i agree too. i would always hav gone with "alternating pd" until i read this thread :confused:

    i think all they really want is to see that you understand the "alternating" part rather than current or voltage etc.
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    (Original post by mik1w)
    maybe Im missing something cos everyone seems to think the exact opposite to me.. but as I understand it,

    current = rate of flow of charge
    therefore a requirement of a current is the movement of charge
    a requirement of a movement of charge is a circuit - a path for charge to follow!

    on the diagram above (http://www.s-cool.co.uk/a-/phy-/part...rtic-dia01.gif) I don't see any circuit! I don't see electrons jumping from A to B or from C to D... how can there be a current when the charge has nowhere to go? each electrode (A,B,C.etc.) is surrounded by air and is a dead end for charge...

    :confused: is there something Im missing.. lol
    the charge changes on the plates. This must mean that the current has an a.c nature.

    Then i realised p.d was alternating => there must be an a.c
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    (Original post by nas7232)
    Describe a linear accelerator. e.g a linac
    6 marks no clarity marks.

    Also, describe a van de graff fully - 5 marks again, no clarity

    past paper questions.
    in a linear accerator, as the charge passes between the tubes, it is accelerated between them, due to the change in the polarity of the tubes as the charge emerges from teh tube...as the velocity of teh electron increases, so too must the distance of the tube so as to ensure that the polarity change is synchronised with the emerging of an electron from the tube. The electric field between the parallel plates causes the particlae to be accelerated, do to the potential difference. The fact that the power supply is important because it needs to be so that the electric fields alternate when the partical appears out of a tube - so as to ensure the particale is always accelerates... (off the top of my head ...so correct me if i'm wrong)

    Van de graff...two domes are next to each other; one has a motor and one is a dome attactched to earth. Turn the power supply on...the belt takes electrons from the lower comb to the upper one, where it is deposited on the dome...as the dome is an insulator, charge builds up on the dome. When the charge built up and has reached its limit, it will start leaking into the surrounding air. Bring the second dome close to the one iwht a motor. Observe teh sparks across the dome...caused by the p.d. caused by the charge difference between the comes.


    not very sure about the van de graff...anyone got any notes on this? Adn how would you attatch a voltmeter to record the voltage across a van de graff thing?

    pk
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    (Original post by Phil23)
    not as stressful as my line up :rolleyes: got Physics synoptic on monday, P4 and P6 maths on tuesday, and M4 on thursday :eek: , and i need A's in the maths for uni, and A in physics for uni as well...aghhh...what is worse, both my firm and insurance want an A in further maths, so i'm screwed if i dont get it - so stressful man!

    Pk
    your schedule looks a bit messed up, bit hard to revise all the A2 modules when they are so close together. Although i had 23 exams this month/last month, my schedule was pretty good.

    Good luck with your exams, im off to revise c4/phy6 all day.
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    I thought a van de graaff worked as follows:

    The belt on the van de graaff acumalates a positive charge by friction, which then repels other positive charges upwards onto the top sphere (Although i guess what its really doing is attracting negatives from the top sphere leaving an excess of positive?). When the Potential difference accross the top sphere and the (earth?) becomes great enough (I think its in the region of MeV?) This ionises the air molecules around the top sphere.

    In the case of the van de graaff in schools i think the positive charge on the sphere attracts electrons from the earth up the second sphere, and when enough air has been ionised, a charge can flow from the negative second sphere through the air to the first positive sphere, causing a spark to show.

    I dont see how this fits in with accelerating particles though, unless you simply place a positive particle (such as an alpha particle) near the positive dome and it gets repelled away?
 
 
 
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