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How to balance the bridge?

Discussion in 'Electronics Homework Help' started by charmcaster.engg, Jan 17, 2015.

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  1. charmcaster.engg

    charmcaster.engg

    79
    1
    Mar 20, 2014
    [​IMG]

    In the given circuit, what is RUNK equal to if RV must be adjusted to 1,232 [​IMG] in order to balance the bridge?
     
  2. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    OK, think about what "balancing the bridge" means. It means that there is no voltage across the meter, right?

    So the left and right hand sides of the bridge are both voltage dividers, supplied from the same source voltage, VS. The right hand side will divide VS by a fixed ratio, which can be calculated from the two resistor values. This will leave a certain proportion of VS across the 100Ω resistor, and the rest across the 560Ω resistor, right? Can you calculate the proportions of VS that will appear across each of those resistors?

    Now you have a voltage divider on the other side as well, and they have told you that when the bridge is balanced, RV is 1232Ω. Can you use the voltage divider formula to calculate what RUNK will be?
     
  3. charmcaster.engg

    charmcaster.engg

    79
    1
    Mar 20, 2014
    I got ratio as 0.178. and the R UNK as 220. Am I right?
     
  4. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

    8,393
    1,268
    Nov 28, 2011
    Yes that's what I get. You've done it an even simpler way than I suggested. It's just all about ratios.
     
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