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Electrical resistance Questionschool experiement ?

  1. Jun 26, 2011 #1
    I'm doing this investigation on RC circuits......we had to find the experimental resistance value of a resistor connected with in the circuit....and a volt meter was connected in parallel with the capictor and resistor.....this question is regarding the resistance of the voltmeter...according to the information we were given, if 10v of pd passes through the voltmeter, the resistance is 100000ohms....so if 20v of pd passes through the voltmeter...would the resistance be 200000ohms???
     
  2. jcsd
  3. Jun 26, 2011 #2

    ehild

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    The internal resistance of the voltmeter does not depend on the measured pd, but changes when you switch over the range. The ohm/volt value of a classical voltmeter is characteristic to the apparatus and does not change when you switch to an other voltage range. It is the maximum reading over the internal resistance. In case the meter is set to 10 V maximum reading, and then the internal resistance is 1000000 ohm, the ohm/volt value is 10000 for that meter. The internal resistance is the same regardless the measured pd, it is 100000 ohm at 1 V or 5 V or 10 V...
    If you want to measure a pd higher than 10 V you need to switch to a higher range. The ohm/volt value of the meter is 10000. If there is a 20 V range, the internal resistance is 200000 ohm here.

    ehild
     
  4. Jul 2, 2011 #3
    Thanks!!! :-)
     
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