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Ammeter and Voltmeter question?

  1. Oct 25, 2011 #1
    1. The problem statement, all variables and given/known data

    A ammeter and a voltmeter are joined in series to a cell . Their reading are A and V respectively. If a resistance is now joined in parallel with voltmeter,
    (a) Both A and V will increase
    (b) Both A and V will decrease
    (c) A will decrease V will increase
    (d) A will increase V will decrease

    2. Relevant equations

    You know that so i needn't to provide

    3. The attempt at a solution

    For me option 'B' is correct
    why?
    because; in first case net resistance in Rv+Ra so current in the circuit is [tex]\frac{V}{Rv+Ra}[\tex] In second case a new resistance is introduced in the circuit so net resistance is Rv+Ra+R. Current in this case is [itex]\frac{V}{Rv+Ra+R}[\itex]. A we can see quit clearly that [itex]\frac{V}{Rv+Ra[/sub}[\itex] > [itex]\frac{V}{Rv+Ra+R}[/itex]
    so current in second case (say I2) is greater than current in first case(say I1)
    Potential difference between the voltmeter in first case is [itex]RvI1[\itex] and in second case is [itex]RvI2[\itex]. I2<i1 so potential difference between the voltmeter in first case should greater than that in second case.
    so what's the conclusion; that is ammeter reading as well as voltmeter reading will drop so. Option B is correct for me.
    As always i ask. where am i wrong?
    sorry friends i tried to change / \ and some others, but none work with tex itex so try understand as it is written or just put answer.
     
    Last edited: Oct 25, 2011
  2. jcsd
  3. Oct 25, 2011 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member

    It is wrong.

    Read the problem again, especially the text in blue. Draw the circuit diagram, and find out how the resistances are connected.

    ehild
     
    Last edited: Oct 25, 2011
  4. Oct 25, 2011 #3
    :smile:thanks buddy:smile:. Question solved.:smile:
     
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