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    I've been stuck on these two questions for 90 minutes now and I'm no nearer to completing it. Can I have some help on how to do these please?

    (a) A battey is used to drive two different load resistors. When it is connected to a 20 ohm resistor a current of 0.10 A is drawn, whereas a load resistor of 80 ohm resistor draws 0.033 A. Determine the e.m.f. and the internal resistance.

    (b) You have a moving coil meter of full scale deflection 50mA and resistance 5 ohms. Explain how you would use it to measure voltages up to 10V determining the values of any components you have used.
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    answer meeeeeeeeeeeeee!!!!!!!!!
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    Just write down what you know and it should become obvious how to proceed.

    (a)
    0.1 = E/(20+r)
    0.033 = E(80+r)

    You now have two equations with two unknowns, so can solve simultaneously.

    (b)
    Just write down what you know again.

    0.05 = 10/(5+R)

    Solve for R and you know that when placed in series with that resistor R, a 10V excitation will cause full scale deflection since 50mA flows.
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    (Original post by EdwardCurrent)
    Just write down what you know and it should become obvious how to proceed.

    (a)
    0.1 = E/(20+r)
    0.033 = E(80+r)

    You now have two equations with two unknowns, so can solve simultaneously.

    (b)
    Just write down what you know again.

    0.05 = 10/(5+R)

    Solve for R and you know that when placed in series with that resistor R, a 10V excitation will cause full scale deflection since 50mA flows.
    ^^This^^

    To OP just in case: if you didn't know already, the formula used here was

    E=I(R-r)

    'E' is e.m.f and 'r' is the internal resistance.

    just rearrange to make I the subject, and Bob's your Uncle.
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    thanks for that, I've managed to solvethe question now

    phew, frustrations gone
 
 
 
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