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OCR Physics A G482, Electrons, Waves and Photons, 25th May 2012

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    Do you guys know which way a diode should point in a circuit? Should we draw it following conventional current or electron flow?
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    (Original post by CharleyChester)
    So yeah, revision is going well:

    The hell is the little bloke at the bottom?
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    (Original post by soulcrasher)
    Do you guys know which way a diode should point in a circuit? Should we draw it following conventional current or electron flow?
    The vertical line represents the cathode of the diode. That end of the diode must face the direction from which the negative current flow is coming.

    http://www.ehow.com/how_5877369_chec...#ixzz1O1lwijrL
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    (Original post by wibletg)
    The hell is the little bloke at the bottom?
    Thats de Broglie
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    (Original post by CharleyChester)
    Thats de Broglie
    Riiight

    He does have some crazy hair, does de Broglie
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    (Original post by wibletg)
    Riiight

    He does have some crazy hair, does de Broglie
    He seemed like the kind of guy to wear a top hat...?
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    (Original post by CharleyChester)
    He seemed like the kind of guy to wear a top hat...?
    Google him, he has some proper funky hair. :cool:
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    For the June 2009 paper, what diagram are we supposed to draw for the circuit in question 1)c)i) since the mark scheme isn't really clear
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    For anyone interested I found a link to some well set out notes for this unit: http://milanmehta.net/ocrphysics/OCR...isionNotes.pdf
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    (Original post by davie18)
    For anyone interested I found a link to some well set out notes for this unit: http://milanmehta.net/ocrphysics/OCR...isionNotes.pdf
    Remind me to pos you tomorrow.
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    (Original post by wibletg)
    Remind me to pos you tomorrow.
    Also you can download it as a word document here if you want to make your own little adjustments.
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    (Original post by davie18)
    Also you can download it as a word document here if you want to make your own little adjustments.
    Cheers, that is one brilliant set of notes.
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    Hey,

    Can someone please explain the origin of absorption and emission spectra. My teacher skipped it and i have no idea what they are or what the difference is.

    Any help is much appreciated

    Thanks
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    (Original post by davie18)
    Also you can download it as a word document here if you want to make your own little adjustments.
    Legend. Will +1 you when i have some to give
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    (Original post by <XOXO>)
    Hey,

    Can someone please explain the origin of absorption and emission spectra. My teacher skipped it and i have no idea what they are or what the difference is.

    Any help is much appreciated

    Thanks
    Emission Spectra
    • Hot gasses produce line emission spectra
    • If a gas is heated, the electrons move to higher levels.
    • As they fall back down to ground state, they emit photons, producing line emission spectra with a black background with bright lines.
    • Each line corresponds to a particular wavelength of light emitted by the source.
    • Since only certain photon energies can be emitted, you only get the corresponding wavelengths.


    Absorption Spectra
    • Cool gasses remove certain wavelengths from the continuous spectrum to produce an absorption spectrum
    • At low temperatures, most of the electrons will be at ground states.
    • Photons of the correct wavelengths are absorbed by the electrons to excite them to a higher energy level.
    • These wavelengths are then missing from the continuous spectrum when it comes from the gas
    • When looking at the sun, we do not see a full spectrum, this is because the light emitted by the sun must travel through the cooler outer layers of the sun’s atmosphere, as a result certain wavelengths are filtered out

    Taken from the word document above
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    Does hot gas just randomly get really excited and emit a photon? As in, the rate of photon emission is randomised?

    Also, which way around do Light dependant resistors and "Heat dependant" resistors resist? eg. do LDRs resist when lots of light are falling on them, or when no light is falling on them?
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    (Original post by ebmaj7)
    Does hot gas just randomly get really excited and emit a photon? As in, the rate of photon emission is randomised?

    Also, which way around do Light dependant resistors and Heat dependant resistors resist? eg. do LDRs resist when lots of light are falling on them, or when no light is falling on them?

    Electrons are normally in the ground state, we say the electrons are in a excited state when they move up to a higher energy level.

    I suggest you watch this video which explains in a simple way, graphically.
    http://www.youtube.com/watch?v=kJBcXFsFa7Y

    LDRs - As the light intensity on the LDR increases the resistance of the LDR decreases.

    Thermistors (Heat dependant resistors lol) - As the temperature increases the resistance of the themistor decreases.
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    did anyone do the January 2011 paper?
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    can someone explain this to me:
    i have heard somewhere that current always stays the same in a circuit and never gets used up.
    but in some questions and diagrams it shows different currents and ... in confusing
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    (Original post by Abused Tampon)
    can someone explain this to me:
    i have heard somewhere that current always stays the same in a circuit and never gets used up.
    but in some questions and diagrams it shows different currents and ... in confusing
    It stays the same in a series circuit but it splits up in a parallel circuit.

    Kirchoff's first law: "The sum of the currents entering a point = the sum of the currents leaving that point".

    So in other words if you have a circuit that then splits into 2, if it had 10A before then it is impossible for them both to have 10A after splitting as this would break Kirchoff's first law.

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Updated: December 11, 2012
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