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    Did any1 else get 7.9x10^-14 ohm metres for the resistivity on the last q?

    And did any1 get 0.77 for the efficiency of the electric motor q? The current and voltage were given along with the mass and height the weight was lifted by...
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    I got something like what you got for the first one... can't remember if there was efficiency question though.
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    (Original post by apixytm)
    I got something like what you got for the first one... can't remember if there was efficiency question though.
    Ah pheww!

    the efficiency question was one of the first ones after the multiple choice section...
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    Did anyone completely finish the exam because there wasn't enough time given, had to rush the last couple of questions.
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    (Original post by apixytm)
    Did anyone completely finish the exam because there wasn't enough time given, had to rush the last couple of questions.
    Yh likewise, I ran out of time towards the end...
    I had to rush the last few questions
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    Hopefully the grade boundaries will be slightly lower than normal because it was a hard exam
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    (Original post by Rumpelstiltskin_)
    Hopefully the grade boundaries will be slightly lower than normal because it was a hard exam
    hope they will... can you estimate what mark would be which grade? I'm unsure right now
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    (Original post by Rumpelstiltskin_)
    Did any1 else get 7.9x10^-14 ohm metres for the resistivity on the last q?

    And did any1 get 0.77 for the efficiency of the electric motor q? The current and voltage were given along with the mass and height the weight was lifted by...
    I got same for resistivity and got 74% something for effeciency

    U know powe input =IV and power output=Fv wher Fis weight
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    What people got for Fw in moments question
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    For the momentum question
    I got carbon atom moves at something like 40m/s
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    How did everyone do the LDR question? Is the circuit going to work as intended?
    :confused::confused:
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    (Original post by yazopt)
    What people got for Fw in moments question
    About 150 to 160 N.
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    Yeah same
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    (Original post by PhysicsGeeker)
    How did everyone do the LDR question? Is the circuit going to work as intended?
    :confused::confused:
    I thought it was LED and not LDR
    As much as I remember question wanted to know: How it doesn't work, why doesn't it work that way and how do you fix it.

    It doesn't work because it's in the reverse bias. Resistance is infinite in that direction.
    To fix. Change the polarisation of the cell in circuit OR connect the LED other way round.
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    um okay so who did the exam that the thread is actually for ?
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    as in the old spec AS exam
    (Original post by Derek12353)
    um okay so who did the exam that the thread is actually for ?
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    For the question about LDR's did u have to talk about electrons being promoted to the conduction band as to why the resistance increases with increasing light intensity?

    I said that basically as the electrons gain energy from light, they are promoted from the valence band to the conduction band (only conduction electrons are free to carry a charge) so there are more collisions between these and the metal atoms therefore the drift velocity is reduced and resistance increases...
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    Woah wait where is LDR coming from... Dang. I think I probably misread the question in rush!

    I saw a LED symbol (with arrows pointing outwards) and battery connected with opposite direction to forward direction of LED
    Or we are talking about totally different question
 
 
 

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