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

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    (Original post by y-1234)
    hey guys, in the spec theres somthing about:
    -the need to know how to discuss the applications of radioactive materials including enviromental and ethical issues????(nuclear decay topic)
    -also for the oscillations topic, explain how damping and the plastic deformation of ductile materials reduce the amplitude of oscillations??
    hel:O
    do you have the hodder book by graham george? theres a section on ductile materials and damping. it says something about ductile materials undergoing the hystersis loop and thereby absorbing the energy from the system
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    (Original post by kosy91)
    do you have the hodder book by graham george? theres a section on ductile materials and damping. it says something about ductile materials undergoing the hystersis loop and thereby absorbing the energy from the system
    could you just quickly remind me what hysteresis is? I've forgotten, and I can't find my notes on it! :eek:
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    (Original post by BPat)
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    thanks
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    (Original post by unamed)
    could you just quickly remind me what hysteresis is? I've forgotten, and I can't find my notes on it! :eek:
    it is when a material like rubber has a force acting on it.First you stretch it (loading)and then release it(unloading).
    when you sketch a graph of stress against strain there is a shape like a loop formed.The work done when stretching is greater than the energy released when unloading and the energy difference is dissipated as heat in the rubber and its temperature rises.(The area within the hysteresis loop represents the thermal energy dissipated in every cycle)

    Remember now?
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    (Original post by fredbraty)
    it is when a material like rubber has a force acting on it.First you stretch it (loading)and then release it(unloading).
    when you sketch a graph of stress against strain there is a shape like a loop formed.The work done when stretching is greater than the energy released when unloading and the energy difference is dissipated as heat in the rubber and its temperature rises.(The area within the hysteresis loop represents the thermal energy dissipated in every cycle)

    Remember now?
    Yes, it's slowly coming back to me! Thank you!
    I think I'll go over materials from last year before I (re)go over this unit's stuff.
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    (Original post by kappleberry)
    I have three days to revsie for this exam. GAH
    Im totally grrd about all that space stuff TIPS TIPS TIPS? =/

    In vain you just missed Olivers revision session on astro he just finished it:rolleyes: :rolleyes:
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    Gotta post loads of MCQs by tomorrow:cool:
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    (Original post by ishta)
    In vain you just missed Olivers revision session on astro he just finished it:rolleyes: :rolleyes:

    Sad times. Nvm, I got a bunch of unanswered Qs to get through by the end of today.





    Kindve confused on one. Not sure what paper this is:
    :mad:

    In reality the temperature drops when going down into the ocean from 25'C at the surface to 10'C. Calculate the % change in the average KE of the air molecules as a result of this temp change.

    Help please?
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    (Original post by kappleberry)
    In reality the temperature drops when going down into the ocean from 25'C at the surface to 10'C. Calculate the % change in the average KE of the air molecules as a result of this temp change.
    Mean kinetic energy, <Ek> = ½m<c2> = 3kT/2.
    So you need (Ek1-Ek2)*100%/Ek1 = (T2-T1)*100%/T1, in Kelvins.
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    (Original post by yadas)
    Mean kinetic energy, <Ek> = ½m<c2> = 3kT/2.
    That's what I used, but theyve just simply turned 'C into Kelvins, found the difference, and then the % diff. Why wouldn't they use the ideal gas formula?
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    Also, what are the conditions for an ideal gas?
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    how do you define a standard candle?
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    (Original post by Kameo)
    how do you define a standard candle?
    a standard candle produces a fixed amount of light, in stars this refers to luminosity. All supernovae have the same quantity of hydrogen and are all undergoing fusion.
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    :hello:

    I have some questions and i would really appreciate it if someone would be kind enough to help me .

    So Tim Akrill,Graham George's book.Page 104.Question 1c)why the answer should be quoted to 2 significant figures?The mass is to 4 significant figures...

    Also,3 a)did it mean 0.25 kg of water?

    Also,question 5.a)we need the rate of rise of temperature at the beginning of the heating process.What is the beginning??what time interval?

    Thank you.Thank you.:yep:
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    (Original post by kappleberry)
    Also, what are the conditions for an ideal gas?

    It obeys the equation pv=NKT under all conditions(under any pressure or temperature)
    :yes: :yes:
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    (Original post by ishta)
    It obeys the equation pv=NKT under all conditions(under any pressure or temperature)
    :yes: :yes:
    Thank youu, but sorry, still really confused. So air isnt an ideal gas-why?
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    (Original post by kappleberry)
    Thank youu, but sorry, still really confused. So air isnt an ideal gas-why?
    Because the particles in the air have mass, they also have little gravitational fields, so the other particles do work in these fields (hence the air particles have potential energy as well as kinetic energy). But ideal gases only have kinetic energy, so air is not an ideal gas.
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    (Original post by kappleberry)
    Thank youu, but sorry, still really confused. So air isnt an ideal gas-why?
    In ideal gases:
    - Molecules have zero size.
    -Molecules are identical.
    -Molecules collide with each other and the walls of their containers without any loss of energy.
    -The collisions take zero time.
    -Molecules exert no forces on each other, except in collisions.
    -There are enough molecules that statistics can be applied.
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    (Original post by kappleberry)
    Thank youu, but sorry, still really confused. So air isnt an ideal gas-why?
    mm no probs actually thats a good question mm I guess we just assume that all gases (including air) is Ideal for the purpose of the calculations.I am not actually sure.
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    (Original post by kappleberry)
    Thank youu, but sorry, still really confused. So air isnt an ideal gas-why?
    There are assumptions for an ideal gases stated above.
    Also nitrogen (80% of air) at 77.36K wants to become liquid..
    And for some reason liquid nitrogen doesnt behave like an ideal gas.
    It also liquifies at very high pressure (if the temperature is kept constant).
 
 
 
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