Hey there! Sign in to join this conversationNew here? Join for free

Edexcel Physics Unit 2 "Physics at work" June 2013 Watch

  • View Poll Results: The last question - Does resistance increase or decrease?
    It increases ( using V=IR or some other method)
    70.73%
    It decreases using the 'lattice vibrations' theory
    29.27%

    Offline

    11
    ReputationRep:
    (Original post by sarah.102)
    Also guys, latest confusion what is potential difference? I understand that it is the measure of energy transfer in between 2 points in an electric circuit or it drives the circuit by forcing the current to flow but still I feel a bit confused. Say if I calculate the potential difference and get 3V what does that actually mean?
    3V means that 3J is work done on a coulomb (bunch of electrons) of charge when passing through a component.
    Offline

    3
    ReputationRep:
    (Original post by sarah.102)
    Also guys, latest confusion what is potential difference? I understand that it is the measure of energy transfer in between 2 points in an electric circuit or it drives the circuit by forcing the current to flow but still I feel a bit confused. Say if I calculate the potential difference and get 3V what does that actually mean?
    The 3V is the energy transferred from the source of energy, EMF. 3V from however much the cell provides to the circuit.
    Offline

    0
    ReputationRep:
    (Original post by krisshP)
    3V means that 3J is work done on a coulomb (bunch of electrons) of charge when passing through a component.
    Yaaa^^
    Offline

    0
    ReputationRep:
    (Original post by B-Stacks)
    The 3V is the energy transferred from the source of energy, EMF. 3V from however much the cell provides to the circuit.
    Thats helped my understanding too, thanksss!
    Offline

    0
    ReputationRep:
    (Original post by sarah.102)
    Also guys, latest confusion what is potential difference? I understand that it is the measure of energy transfer in between 2 points in an electric circuit or it drives the circuit by forcing the current to flow but still I feel a bit confused. Say if I calculate the potential difference and get 3V what does that actually mean?
    A potential difference of 3Volts means 3 joules is given to every coloumb of charge, to push it around a circuit. Now if you used 10 volts, you'd give 10 joules to every coloumb, so the current would get a bigger 'push'. But it's important to remember PD is NOT a force, it's just a transfer of energy.
    Offline

    0
    ReputationRep:
    I dont understand part (b). On the mark scheme it says that after doing E=hf you have to divide Power(10W) by th energy found. why?
    Name:  Captura.PNG
Views: 165
Size:  20.9 KB
    Offline

    0
    ReputationRep:
    (Original post by KBenzema)
    I dont understand part (b). On the mark scheme it says that after doing E=hf you have to divide Power(10W) by th energy found. why?
    Name:  Captura.PNG
Views: 165
Size:  20.9 KB
    If you don't remember it it's also on the formula sheet, E = hf, the energy of a photon is equal to Plank's constant times its frequency. I've put the rest in spoiler tags, see if you understand it more before looking at the next hint.

    Spoiler:
    Show
    So, by doing 5.5*1014 (the frequency in Hz given in the question) times 6.63*10-34 (Plank's constant) you get the energy of the photon, roughly 3.65*10-19 Joules.


    Spoiler:
    Show
    Now that you know each photon has 3.65*10-19J of energy you can do 10W divided by 3.65*10-19J to tell you how many photons are emitted per second (W/J = J/s / J = *something*/s, in this case photon/s).


    Spoiler:
    Show
    This would tell you that you would have roughly 2.74*1019 photon's being emitted by the screen per second.
    Offline

    1
    ReputationRep:
    Can somebody please explain to me polarisation? It baffles me for some reason. Reading more and more into it has confused me.
    Offline

    15
    ReputationRep:
    (Original post by sarah.102)
    Can somebody please explain to me polarisation? It baffles me for some reason. Reading more and more into it has confused me.
    Spoiler:
    Show

    For polarization what you need to know is that when light passes through a polarizing filter it will become partially polarized meaning the polarizing filter will only let through light which is acting in the same plane, all other planes of light will be blocked up.

    However when you pass partially polarized light through a second polarizing filter, the intensity of light will depend on the angle the second filter is rotated. It is denoted by equation I = Io cos^2(pheta)
    Where:
    - Io is the initial intensity (after passing through the first filter)
    - I is the final intensity (after passing through the second filter)
    - Pheta is the angle of rotation of the second filter.

    Here you would note that if 2nd filter isn't rotated, such that the angle is 0 degrees light would have full intensity. Since cos 0 = 1. 1 squared = 1.

    If the 2nd filter is rotated perpendicular to the first filter, such that the angle is 90 degrees no light will pass through. Since cos 90 = 0. 0 square = 0.

    Also if the 2nd filter is parallel to the first filter, such that the angle is 180 degrees the light would have full intensity. Since cos 180 = -1. And -1 squared = 1.
    Offline

    18
    ReputationRep:
    (Original post by Boy_wonder_95)
    x
    iirc Malus's law isn't in the Edexcel syllabus, but I could be wrong. May still be useful though :dontknow:
    Offline

    0
    ReputationRep:
    (Original post by justinawe)
    iirc Malus's law isn't in the Edexcel syllabus, but I could be wrong. May still be useful though :dontknow:
    Who's law?? :confused::confused::confused::confused:
    Offline

    11
    ReputationRep:
    (Original post by sarah.102)
    Can somebody please explain to me polarisation? It baffles me for some reason. Reading more and more into it has confused me.
    read this
    http://www.thestudentroom.co.uk/show...352&p=42866490
    Offline

    4
    ReputationRep:
    I think I have discovered the angriest Physics lecturer ever.
    Offline

    0
    ReputationRep:
    i have a big doubt on part (a)(iii)
    why do i get a different answer depending on the formula i use. im baffled.
    P=IV : (0.75)*3=2.25w
    P=I^2R : (0.75)^2*3.6 = 2.025w
    P=V^2/R : (3)^2/3.6 = 2.5w
    Name:  Captura.PNG
Views: 263
Size:  25.7 KB
    Offline

    11
    ReputationRep:
    Can somebody help me with section a question 7 on paper January 2012 unit 2 please? I don't get it at all

    V=IR
    I=V/R

    There's constant pd so surely as R increases, I decreases linearly, giving B as the answer?

    Thanks
    Offline

    11
    ReputationRep:
    In January 2012 paper unit 2 q18a, they said core - cladding. Does this means that light travels from core into cladding, or light travels from cladding? HOW do you know?

    Thanks
    Offline

    14
    ReputationRep:
    (Original post by krisshP)
    3V means that 3J is work done on a coulomb (bunch of electrons) of charge when passing through a component.
    Difference between pdf/voltage and emf
    Offline

    18
    ReputationRep:
    (Original post by avipsita)
    Who's law?? :confused::confused::confused::confused:
    Well, as I said, I'm pretty sure it's not in the Edexcel syllabus.

    It's basically the equation the guy I quoted posted.
    Offline

    11
    ReputationRep:
    (Original post by Daniel Atieh)
    Difference between pdf/voltage and emf
    :confused:?
    Offline

    14
    ReputationRep:
    (Original post by krisshP)
    :confused:?
    lol
    better way:
    1) define voltage
    2) define pdf
    3) define emf

    haha yea it looks weird ..i just noticed
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Has a teacher ever helped you cheat?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • 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.