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    I don't really get 7b part 3 where you have to find out the emf of the battery supply could anyone help me out.

    The answers for the rest are follows:

    Resistance= 0.98 ohms

    Current= 2.08 A

    Voltage= 2.04 V


    Could anyone please help me find the emf, none the equations I try actually work?? The question is in the attachment!




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    ANYONE!!!


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    Well, P = IV, So the EMF = Power (in watts) / Current (in amperes)

    Edit: Not quite sure what you're asking for?

    The EMF (in Volts) = P/I = 4.25/2.08 = 2.04 as you originally stated
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    What equations are you using that don't work?

    V = E - Ir

    V = pd across the external circuit (V)
    E = emf of the cell (V)
    I = current through the cell (A)
    r = value of the internal resistance (Ω )
    (Ir = the p.d. across the internal resistor)

    V = E - Ir
    2.04 = E - (Ir)
    2.04 = E - (2.08x0.98)
    2.04 = E - 2.0834
    E = 2.04 + 2.0834
    E = 4.1234



    I have no idea if that's right... I managed to grab an A in Physics but that was over 7 years ago haha!
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    Look at the second. Photo attachment thats the question! The answer in the mark scheme is 16.1 V


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    Well I got 4.1234v.... Just multiply my answer by 4 and you've got 16.4v which is close enough!

    I'm sure someone who can actually help you will be here soon!
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    (Original post by Rybee)
    Well I got 4.1234v.... Just multiply my answer by 4 and you've got 16.4v which is close enough!

    I'm sure someone who can actually help you will be here soon!
    Its a pretty weird question as you cant use any of the emf equations really need help on this


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    Anyone!!!


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    There are two wires going around the circuit, this surely means they are parallel wires? Does that help?
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    (Original post by raiden95)
    There are two wires going around the circuit, this surely means they are parallel wires? Does that help?
    So how do you find the emf?

    The equation for emf is E = V + Ir and you don't have internal resistance


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    (Original post by Jimmy20002012)
    So how do you find the emf?

    The equation for emf is E = V + Ir and you don't have internal resistance


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    Maybe there is no internal resistance? Do you have resistance in each wire? Do you have overall current?
    Work out total resistance in parallel, then use E=IR

    I'm not 100% sure this is correct, but after i left the exam in january I wish i did this.

    EDIT: sorry about the mistake, the internal resistance is in the copper wire i believe, and the total internal resistance 1/r = 1/0.98 + 1/0.98 is it not?

    Let me know how you do, that's how I think its done my answer is 3.06V or 13.0V, do you know the answer?
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    (Original post by raiden95)
    Maybe there is no internal resistance? Do you have resistance in each wire? Do you have overall current?
    Work out total resistance in parallel, then use E=IR

    I'm not 100% sure this is correct, but after i left the exam in january I wish i did this.

    EDIT: sorry about the mistake, the internal resistance is in the copper wire i believe, and the total internal resistance 1/r = 1/0.98 + 1/0.98 is it not?

    Let me know how you do, that's how I think its done my answer is 3.06V or 13.0V, do you know the answer?
    The answer is 16.1v and the solution is that they do:

    12 + 2 x 2.04 = 16.1 V

    No idea what you do


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    The lamp is working at rated capacity so you've got 12v across the bulb and 2.04v across each of the two wires connecting it to the power supply.
    Seems straightforward tbh.
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    (Original post by Jimmy20002012)
    The answer is 16.1v and the solution is that they do:

    12 + 2 x 2.04 = 16.1 V

    No idea what you do


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    Haha thats weird, i said 3.06 or 13.0 add them its 16.06 which is 16.1 1dp
    :confused:
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    (Original post by raiden95)
    Haha thats weird, i said 3.06 or 13.0 add them its 16.06 which is 16.1 1dp
    :confused:
    There is 12V across the source, as stated in the question. Then, visualise the circuit, paying particular attention to the way that the wires are organised (parallel/series). Then use the appropriate circuit rules to work out the total emf, which is the solution as given. I did this paper in January and got above 90%.
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    (Original post by American Vampire)
    There is 12V across the source, as stated in the question. Then, visualise the circuit, paying particular attention to the way that the wires are organised (parallel/series). Then use the appropriate circuit rules to work out the total emf, which is the solution as given. I did this paper in January and got above 90%.
    Haha same! I got 94% but if i got this question right would have been better!
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    90% and 94% that is amazing, what tips could you give me in order to get that? I got 55/70 which was 1 mark of an A which was annoying, I found out I got full marks in the quantum and particles bit and totally messed up in the electristy bit


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    (Original post by Jimmy20002012)
    90% and 94% that is amazing, what tips could you give me in order to get that? I got 55/70 which was 1 mark of an A which was annoying, I found out I got full marks in the quantum and particles bit and totally messed up in the electristy bit


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    Same really, had full marks up till Q4, lost 2 marks on the question above, other 4 here and there worded questions. Tips would be just make sure you really understand everything going on in a circuit, I myself didn't completely know which is why i lost marks
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    Would you mind attaching the mark scheme here?
 
 
 
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