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Homework Help: What is the resistance of R1

  1. Apr 1, 2010 #1
    1. The problem statement, all variables and given/known data

    The figure shows a dual range dc milliammeter which has a common negative terminal A and positive terminal B and C . The indiacator is a moving coil meter of resistance 50 ohm which gives full scale deflectino with a current of 1.0 mA . When connection ismade with the terminals A and C , a current of 20 mA gives full scale deflection . What is the resistance of R1 ?

    2. Relevant equations

    3. The attempt at a solution

    when A and B are connected to a circuit , R1+R2=50 ohm

    when A and C are connected to a circuit ,

    1mA will flow through the resistor R2 , then to the meter while 19 mA will flow through resistor R1 .

    and pd across meter = pd across shunt

    1(50)=19R1+R2 ---1

    R1+R2=50 ----2

    and R1=0 ??

    Cant be !

    Attached Files:

  2. jcsd
  3. Apr 2, 2010 #2
    Re: meter

    is there anything wrong with my work ?
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