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AQA Physics PHYA5 - 28th June 2016 [Exam Discussion Thread] watch

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    2014 talks about binding energy. A neutron won't have binding energy because it's already unbound I.e, you don't need energy to break it as its already a nucleon.

    2011 talks about mass. You need the mass of the neutron you work out the mass defect overall. In 2014 you didn't need to do this because the total binding energy difference of the reaction is the mass defect.

    Hope it makes sense.
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    (Original post by particlestudent)
    Can someone explain the nuclear radius experiment briefly to me, I don't understand the graph minima at all
    Which graph are you talking about? lnR against lnA ?
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    What do we need to know about CCD's (Option A)
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    this unit is sooooooo hard mann
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    For part b, why would you not use the rest energy of the neutrons in the subtraction?
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    (Original post by ManOfJustTin)
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    For part b, why would you not use the rest energy of the neutrons in the subtraction?
    Neutrons do not have a binding energy.
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    (Original post by rory58824)
    Neutrons do not have a binding energy.
    Is there a specific rule for when you include particles like electrons, protons and neutrons and when you don't?
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    For June 13 Section B Astrophysics, question 2)c)ii) why is the angle subtended (Schwarzschild radius/ distance) instead of (2 * Schwarzschild radius/ distance) to get the diameter which gives 2.5 times instead of 5 times...? Thanks!
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    (Original post by Whizbox)
    Any turning points 6 marker predictions? Motivation for this exam is at a new low, just one more
    I can see an electron microscope 6 marker coming up maybe? like explain all the different parts ..

    Or maybe discharge tubes, that'd be cool..
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    (Original post by Protoxylic)
    Oh yeah of course, but the neutron itself has no binding energy as it's unbound
    my bad i got muddled
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    (Original post by Whizbox)
    Is there a specific rule for when you include particles like electrons, protons and neutrons and when you don't?
    Generally if you're given the masses you should include protons, neutrons or electrons. I suggest reading the information carefully because they sometimes give the mass of the nucleus or the mass of the atom. If it's the mass of the atom, you may have to consider the mass of the number of electrons.
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    I'm more ****ed for this exam than I was for every other exam, the problem of this exam being the last one is that I put revision off for this for ages lmao
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    (Original post by ChronicBoredom)
    Could anyone pleeeease explain to me how you know what the nature of radiation emitted is from different things? E.g. moderators nucleus, spent fuel rods, fission fragments, nuclear reactor core?
    Basically anything that absorbs neutrons becomes neutron rich and unstable. Neutron rich isotopes (to the left and above N vs A graph) decay via beta minus.

    Any isotopes that are excited will reduce their energy by emitting gamma. Nuclei get excited by colliding with high energy neutrons. Any nuclei that emit or capture electrons will also be in an excited state.

    Proton rich (technically neutron deficient) nuclei decay via beta plus (i cant think of a scenario that produces a proton rich isotope). These isotopes sit below and to the right of the N vs A graph.

    So the examples in your question:

    Moderators
    Well what to they do? They are there to collide with high energy neutrons to reduce the kinetic energy of the neutrons. Energy transfer results in excited nuclei. They also absorb neutrons occasionally which result in neutron rich isotopes.

    Spent fuel rods and fission fragments
    If you look at the N vs Z graph. The ratio of N/Z is higher for larger nuclei. Now imagine that If you halve that nucleus, its ratio will basically be the same, this means its N/Z will be higher than its stable isotope (above the stable isotope). Too many neutrons result in instability, neutron rich isotopes will decay via beta minus.

    Reactor core
    Well the reactor core is made up of large unstable nuclei such as Uranium, any nuclei with a proton number above 80 are alpha emitters so Core emits alpha radiation
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    (Original post by splashywill)
    Which graph are you talking about? lnR against lnA ?
    No that detector reading on y axis against the angle of diffraction for the electron diffraction experiment
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    (Original post by rory58824)
    Generally if you're given the masses you should include protons, neutrons or electrons. I suggest reading the information carefully because they sometimes give the mass of the nucleus or the mass of the atom. If it's the mass of the atom, you may have to consider the mass of the number of electrons.
    So if they give you the mass of the atom am I right in saying you need to take away the mass of the electrons?
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    Can someone explain what the avagadro constant is and how to use it?
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    http://filestore.aqa.org.uk/subjects...W-QP-JUN11.PDF
    http://filestore.aqa.org.uk/subjects...W-MS-JUN11.PDF
    Question 4b, it says "for a further 500 s", doesn't that mean we have to take the energy we calculated in the first part into account as well as the energy required to change the state, yet the mark scheme doesn't take in account the former. Why is that?
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    (Original post by Whizbox)
    So if they give you the mass of the atom am I right in saying you need to take away the mass of the electrons?
    That's usually the case, yes, but that obviously depends on what they're asking.
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    (Original post by rory58824)
    That's usually the case, yes, but that obviously depends on what they're asking.
    Is there a question in a past paper like that?
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    (Original post by Whizbox)
    Is there a question in a past paper like that?
    To my surprise, no. In the textbook try question 2(b) on page 195.
 
 
 
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