Turn on thread page Beta

Edexcel A2 Physics Unit 5 'Physics from Creation to Collapse' watch

    Offline

    0
    ReputationRep:
    (Original post by BPat)
    I think there will be quite a big question on Thermal Physics.

    Probably a 5 mark one on life cycle of a star.

    I hope i don't panic as much as i did in the Unit 4 Jan paper.
    Did you try out the Sample for UNIT 5 (6PHO5/1) ?
    wat'd you get ?
    Offline

    2
    ReputationRep:
    (Original post by samydude)
    I completely agree. SHM is a bit dodgy.



    The fusion of iron would subtract energy rather than provide it. (Endothermic).

    ... That didn't answer your question, but what the hey
    ... I don't think u need to know that.
    If I write this word in the exam, and it turns out I was wrong, you are responsible. :mad:
    Offline

    0
    ReputationRep:
    (Original post by Kameo)
    If I write this word in the exam, and it turns out I was wrong, you are responsible. :mad:
    What, ?:eek: NO! - ENDOTHERMIC is correct.
    Well I just had a read -

    "To fuse iron into heavier elements requires more energy than is released by the fusion reaction, thus making the reaction unsustainable.
    Every element heavier than Iron is created in a stellar explosion (Supernova)."
    Offline

    2
    ReputationRep:
    (Original post by samydude)
    What, ?:eek: NO! - ENDOTHERMIC is correct.
    Well I just had a read -

    "To fuse iron into heavier elements requires more energy than is released by the fusion reaction, thus making the reaction unsustainable.
    Every element heavier than Iron is created in a stellar explosion (Supernova)."


    why is this?
    Offline

    4
    ReputationRep:
    (Original post by samydude)
    Did you try out the Sample for UNIT 5 (6PHO5/1) ?
    wat'd you get ?
    52%. :o:

    But i did the spec paper ages ago and it was to see what topics i struggle with. I'll probably do it again tonight or tomorrow to see if i've improved.
    Offline

    4
    ReputationRep:
    (Original post by Kameo)
    Why is Iron the limit for nuclear fusion?
    I started a thread about this:

    http://www.thestudentroom.co.uk/show....php?t=1318560

    Its got a few good responses there, hope it helps.
    Offline

    0
    ReputationRep:
    (Original post by Kameo)
    [/B]

    why is this?
    Because GOD wants it to happen.
    Offline

    1
    ReputationRep:
    Does anyone have the formula sheet we'll be given in the exam?

    Also - Will we need to know how to many metres are in a parsec or an AU? Because my book talks about them but I was wondering if we need to convert, that they might just tell us how many metres are in them on the exam paper.
    Offline

    0
    ReputationRep:
    (Original post by Sasukekun)
    Does anyone have the formula sheet we'll be given in the exam?

    Also - Will we need to know how to many metres are in a parsec or an AU? Because my book talks about them but I was wondering if we need to convert, that they might just tell us how many metres are in them on the exam paper.
    I think we will be given the value of AU if we require it.
    Though we can remember it, as it's 1.5*1011m, not that difficult.
    And from this we can derive the value of a parsec.
    Attached Files
  1. File Type: docx Formulae sheet.docx (19.4 KB, 135 views)
    Offline

    1
    ReputationRep:
    Yes it's not difficult, but it's worthless spending my time trying to remember it if we're just given it.
    Offline

    0
    ReputationRep:
    (Original post by Sasukekun)
    Does anyone have the formula sheet we'll be given in the exam?

    Also - Will we need to know how to many metres are in a parsec or an AU? Because my book talks about them but I was wondering if we need to convert, that they might just tell us how many metres are in them on the exam paper.
    http://www.edexcel.com/migrationdocu...4%20260510.pdf

    Page 172
    Offline

    0
    ReputationRep:
    (Original post by Kameo)
    Why is Iron the limit for nuclear fusion?
    Since Fe has the highest binding energy per nucleon, making it the most stable element! therefore fusion will not proceed after producing the element Fe !
    The fusion of iron would subtract energy rather than provide it
    Offline

    0
    ReputationRep:
    (Original post by Sasukekun)
    Yes it's not difficult, but it's worthless spending my time trying to remember it if we're just given it.
    After solving a few dozen questions on astrophysics it just stuck in my head.
    Offline

    7
    ReputationRep:
    ^^Yadas...thank yuuuuu
    Offline

    7
    ReputationRep:
    (Original post by yadas)
    Definitely damping doesnt change the natural frequency.
    That means damping doesnt change the frequency at which maximum energy is absorbed by the oscillating system.
    Though damping decreases the frequency at which maximum amplitude occures.
    So it doesnt change the frequency at which energy resonance occures,
    but it does change the frequency at which amplitude resonance occures.
    A pic from wiki.


    (ii)
    Data provided:
    ro = 7.0*105m
    ro = 1.06r => r = ro/1.06 = 6.6*105m
    A = 4пr2 = 5.48*1012m2

    (iii)
    Lo = 1.4L
    ro = 1.06r
    To = 5800K
    Lo = 4пσro2To4 ; A
    L = 4пσr2T4 ; B
    Dividing A by B gives
    1.4 = 1.062To4/T4
    (To/T)4 = 1.4/1.062 ; taking the fourth root of each side
    To/T = 1.0565
    T = To/1.0565 ≈ 5500K
    So To - T ≈ 300K.

    (iv)
    ƛmaxT = 2.898*10-3
    ƛmax = 2.898*10-3/T
    ƛmax = 2.898*10-3/T ≈ 5.27*10-7m (= 527nm)
    ƛmax o = 2.898*10-3/To ≈ 5*10-7m (= 500nm)
    Δƛ = ƛmax - ƛmax o ≈ 527 - 500 = 27nm = 2.7*10-8m.
    hey sorry, you know in part (ii), to find the inc in temp, why cant we just use the new values for L and A to get T?
    Offline

    0
    ReputationRep:
    (Original post by kappleberry)
    hey sorry, you know in part (ii), to find the inc in temp, why cant we just use the new values for L and A to get T?
    You mean part (iii), right?
    We could do that, but we would first need to find the values for L and A (from Lo and Ao), and express T in terms of To.
    You are free to use any way you find easier/faster.
    Offline

    7
    ReputationRep:
    (Original post by yadas)
    You mean part (iii), right?
    We could do that, but we would first need to find the values for L and A (from Lo and Ao), and express T in terms of To.
    You are free to use any way you find easier/faster.
    Cant we use the values of L and A that weve just found in the previous parts? What we need is the inital T, and since weve been given the current T..just subtract?

    Am i missing something?
    The way Im doing it..tis not workiing.=/
    Offline

    13
    ReputationRep:
    I understand everything except for SHM
    Offline

    0
    ReputationRep:
    (Original post by yadas)
    Definitely damping doesnt change the natural frequency.
    That means damping doesnt change the frequency at which maximum energy is absorbed by the oscillating system.
    Though damping decreases the frequency at which maximum amplitude occures.
    So it doesnt change the frequency at which energy resonance occures,
    but it does change the frequency at which amplitude resonance occures.
    A pic from wiki.
    Top stuff as usual but are you implying that maximum amplitude happens at a specific frequency?
    Offline

    0
    ReputationRep:
    (Original post by lefneosan)
    Top stuff as usual but are you implying that maximum amplitude happens at a specific frequency?
    Without damping this specific frequency is natural frequency of the oscillating system, obviously.
    Damping reduces the frequency at which maximum amplitude is possible.
    Increasing damping further reduces this frequency, as you can see from the picture.
    Thought the maximum energu would still be absorbed at natural frequency, even with damping.

    (Original post by kappleberry)
    Cant we use the values of L and A that weve just found in the previous parts? What we need is the inital T, and since weve been given the current T..just subtract?

    Am i missing something?
    The way Im doing it..tis not workiing.=/
    Are you taking the fourth root of T4?
    Using L = 2.8*1026, A = 5.5*1018 and σ = 5.67*10-8, gives a value of T4 as 8.93*1014.
    The fourth root of that is about 5470K.
    (5800 - 5470 = 330, can be rounded to 300.)
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: March 27, 2015

University open days

  1. University of Cambridge
    Christ's College Undergraduate
    Wed, 26 Sep '18
  2. Norwich University of the Arts
    Undergraduate Open Days Undergraduate
    Fri, 28 Sep '18
  3. Edge Hill University
    Faculty of Health and Social Care Undergraduate
    Sat, 29 Sep '18
Poll
Which accompaniment is best?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.