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Homework Help: Questions Considering General Circuits

  1. May 8, 2013 #1
    Hey everyone,

    I'm currently working through some physics questions considering physics and became really stuck over a few questions therein.

    1: If you have a circuit (See file 1) where the ammeter reads 3.20 then what will the voltmeter read?

    2: If you have a circuit (See file 2) where the resistance points are 4, 2, and 2, ohms then what will the equivalent resistance be between points A and B.

    3: If you have a bridge circuit (See file 3) where I=6A, I2=4A, and I3=0 then find I1, I4, and I5.

    As far as I'm concerned these questions are supposed to be really easy and are to be solved using the basic principals of physics but try as I might I just cant understand where to start. If you could provide some detailed solutions as to how I might solve them then that would be awesome. Btw these questions are on a grade 12 scale (just to give you guys an idea of what I'm working on). Thanks!

    Attached Files:

  2. jcsd
  3. May 8, 2013 #2


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    Start with equations about electric circuits and objects in them. Try to apply them in your circuits and see what you get. This works. Always.
  4. May 8, 2013 #3
    Yes, but how do I know which ones to use? Eg, in the second question I don't even know if the circuit is considered a parallel or series circuit! Which one do you think it is?
  5. May 8, 2013 #4


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    Experience, or trial and error. There is no way to get experience without solving those problems yourself.

    Split the problem into smaller parts then.
    Do you see some resistors which are in parallel? That means that you have two resistors where the corresponding sides are connected.
    Do you see some resistors which are in series? That means that you have two resistors in a line without a branch in between.
  6. May 8, 2013 #5


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    Ohms Law is a good place to start, specially for circuit 1 and 2

    V = I x R

    1) a hint All the resistors are in parallel across the battery, so the voltage across each resistor is going to be the same

    2) work out the total resistance on the bottom line, the 2 x series resistors then you now will have 2 resistors in parallel
    Then use the parallel resistor calculation to work out the total resistance ... google search "parallel resistors"

    The first 2 ARE really easy, the third diagram takes a bit more effort

  7. May 8, 2013 #6
    Lol, yeah, I figured that out as I was doing some research on the web. :) Thanks for the reply!

    By the way, how should I start on question 3?
  8. May 9, 2013 #7


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    With Kirchhoff's laws.
    Do you know the resistances of the resistors (or at least the relative resistances)?
  9. May 10, 2013 #8


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    Start by dwelling on the implications of being told that I3=0
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