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    Hi I need some help with this physics question




    From the circuit in the figure calculate the following:

    a) Currents through resistors R1, R2 and R3
    b) Power dissipated in R3



    Note: values of the resistances are in Ohms.



    im stuck on a and b... please help!
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    For A:
    R1, R3: 10 = I(3 + 7)
    I = 1A

    R2, R3: 5 = I(3 + 14)
    I = 0.29A
    Just one more step to work out the current of each resistor.


    For B:
    Use v = IR with the current from A.
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    hey! what do you mean one more step for question a.. dont get that part
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    (Original post by SpikeSpiegel)
    hey! what do you mean one more step for question a.. dont get that part
    You have IR1 and IR2.
    IR3 = IR2 + IR1.
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    Cool ... thank you so much!!!!
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    For part a) i got

    a) R1, R3 : 10 = I(3+7)
    Therefore I = 1A


    R2, R3 : 5 = I(3+14)
    I= 0.29 A


    I have - IR1 and IR2
    : IR3 = IR2 + IR1

    So, R3 = R1+R2
    R3= 1A + 0.29A = 1.29A



    is this how I would approach this?


    I don't know how to go about part b since there is 2 voltages for R3
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    (Original post by SpikeSpiegel)
    For part a) i got

    a) R1, R3 : 10 = I(3+7)
    Therefore I = 1A


    R2, R3 : 5 = I(3+14)
    I= 0.29 A


    I have - IR1 and IR2
    : IR3 = IR2 + IR1

    So, R3 = R1+R2
    R3= 1A + 0.29A = 1.29A



    is this how I would approach this?


    I don't know how to go about part b since there is 2 voltages for R3
    Yes.

    For b, use v = IR, you know I and R.
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    but it asks for power dissipated ... not voltage?
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    (Original post by SpikeSpiegel)
    but it asks for power dissipated ... not voltage?

    Sorry I didn't read that part of the question properly, but the idea is the same. There are two equivalent methods:
    1. Calculate voltage as I said and use p = Iv.
    2. Use p = I2R.
    I would go with 2.
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    so.. this is how i did it

    p= I^2 R

    p= 1.29 x 3

    so, p = 3.87?
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    (Original post by SpikeSpiegel)
    so.. this is how i did it

    p= I^2 R

    p= 1.29 x 3

    so, p = 3.87?
    You forgot to square the I
    It should be p = 1.292x3=4.9923W
 
 
 
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