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Homework Help: Measurements with an Ammeter/Voltmeter

  1. Dec 18, 2009 #1
    1. The problem statement, all variables and given/known data
    1) What is needed for an ammeter to measure current accurately?
    2) What is needed for a voltmeter to measure the potential differences in the circuit accurately?

    3) How can you construct an ammeter from a resistor and a galvanometer?
    4) How can you construct a voltmeter from a resistor and a galvanometer?

    2. Relevant equations



    3. The attempt at a solution
    For 1 & 2, I just want to make sure I’m not missing any major reasons. An ammeter should have a resistance as close to 0 as possible and should be connected in series. A voltmeter has a theoretical resistance of infinity and should be connected in parallel.

    3 & 4 have me confused... I thought a galvanometer was equivalent to an ammeter! Can you just pick a galvanometer with the appropriate resistance and hook it up properly?
     
  2. jcsd
  3. Dec 19, 2009 #2

    ehild

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    Homework Helper

    A galvanometer can measure very low current and voltage values, in the range of micro amps and millivolts. If you want to measure higher current and voltage, you have to extend the range of the galvanometer, by ensuring that no higher than the allowed current flows through it. By connecting a resistor parallel with the galvanometer, part of the current will flow through this parallel resistor, called shunt. f you want to measure voltage, you need to connect a resistor in series with the galvanometer so as part of the voltage should drop across this multiplier.

    ehild
     
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