Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: 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
    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


    User Avatar
    Homework Helper

    It is wrong.

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

    Last edited: Oct 25, 2011
  4. Oct 25, 2011 #3
    :smile:thanks buddy:smile:. Question solved.:smile:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook