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Homework Help: Circuit Analysis Problem

  1. Oct 28, 2012 #1
    Hi there,
    I have difficulties with the last 2 parts of the question - b) and c)

    3. The attempt at a solution
    I think I found the right values for I1, I2 , I3
    I1 = 1A
    I2 = I3 = 0.5A
    Voltage drops V1 - V4 using E=I * R (16,16,8,8,16,8)
    Powers - 16,4,8,4,8,8


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  2. jcsd
  3. Oct 28, 2012 #2


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    I agree.

    V1 to V4 I made 16, 16, 16, 8 Volts Note V3 is across R5 not R3, V4 is across R6 not R4
    P1 to P6 I made 16, 8, 4, 4, 8, 8 Watts Total = 48W.

    Power from Battery = Vbat * Ibat = 48V x 1A = 48W eg same as dissipated in the R's.

    b) Hint: remember that energy = power * time

    c) Hint: A 60AH (AH =Amp Hour) battery can deliver 60A for one hour or pro rata.
  4. Oct 29, 2012 #3
    Thanks for the reply!

    I've just rewritten the values incorrectly..
    For b) I found that for 30min it the value will be 1440 and for an hour 2880 but dont know how to end up with a good conclusion.
    And still wondering for c) so these 60Ah will be enough for a little more than an hour?
  5. Oct 30, 2012 #4


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    b) You made a small mistake. Time has to be in seconds not mins.

    The battery delivers 1A at 48V for 30min. The power is therefore 48W.

    Energy(Joules) = Power(Watts) * Time(seconds)

    = 48 * 30 * 60
    = 86400 Joules.

    c) If the battery has a capacity of 60AH it can in theory deliver 60A for 1 hour or 1A for 60 Hours (or any other product that equals 60). If the circuit only draws 1A the battery could power it for 60 hours.

    Since in part b) the circut draws 1A for 0.5 hour it has consumed only 1 * 0.5 = 0.5AH. You can work out the percentage. It's less than 1%.
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