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Formula to get voltage on circuit

Discussion in 'Electronics Homework Help' started by olakease, May 12, 2014.

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  1. olakease

    olakease

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    May 12, 2014
    Maybe this is a Do my Homework question, but I'm learning Electronics and I'm confused on solve a simple Circuit.

    The value in Voltimeter is 2.25 V, but, how can I get this value with Analysis? I mean, exists a formula for this?
    [​IMG]
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Yes, this does look like a homework question. I've moved it to the homework forum.

    The first thing to do is to redraw that confusing diagram in a more familiar way.

    268589.gif

    Now you can see that the batteries are in series, and the resistors form a voltage divider across their combined voltage.

    If you use the bottom line of the diagram as the 0V reference, you should be able to figure out the voltages on each side of the "V?" marking, and confirm that the difference between them is 2.25V. Then try to convert the formulas you used to calculate the voltages on each side, into a single formula that calculates the voltage difference.

    I've identified the two voltage sources and the two resistors. Your formula should use those references, so that you can change the voltages and/or the resistances and the formula will still work.
     
    olakease likes this.
  3. nges

    nges

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    Feb 21, 2014
    the value on the meter can be calculated using thevenin or norton or millman or .. theorems. but using the millmans method we have:

    Vm= (6/5-1.5/5)/(1/5+1/5)=(6*5+5*1.5)/(5+5)=2.25V
     
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  4. olakease

    olakease

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    May 12, 2014
    Thank you for your replies, I will apply this.
     
  5. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Or what about (6V-1.5)/2 = 2.25V. Subtract the lower battery voltage from the top battery and replace the bottom battery with a short. Then you just have to work out the potential where the two resistors are joined in the middle with respect to 0V. This is just a simple potential divider and because the two resistors are the same value it is just the new battery voltage 4.5Volts divided buy 2.
    Thanks
    Adam
     
  6. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
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    Nov 28, 2011
    As you can see, there are several ways of looking at this problem. My brain works best when I can identify a 0V rail, and it's the most negative part of the circuit (in most cases), so all other voltages are positive (or at least, non-negative) relative to it. Which approach is best depends on how you think, I guess.
     
  7. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    I am the same as you Kris.
     
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