little question

Discussion in 'Homework Help' started by Musab, Sep 20, 2008.

  1. Musab

    Thread Starter Member

    Sep 20, 2008
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    in a simple resistors circuit, why the measured value is always slightly less than the calculated value ?
     
  2. bertus

    Administrator

    Apr 5, 2008
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    Hello,

    When you measure inside a circuit, it can be that other components are parallel to the resistor so the value you measure is lower.

    Greetings,
    Bertus
     
  3. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    The best way to measure the value of a resistor that is part of a circuit is to lift or otherwise disconnect the resistor at one end and then measure it.

    hgmjr
     
  4. Musab

    Thread Starter Member

    Sep 20, 2008
    25
    0
    but even if there are no other components. Just resistors in series or parallel, the value is still slightly less
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    Often there is a sneak current path around the resistor being measured. By disconnecting one end you can insure that the only current path seen by the meter is through the resistor being measured.

    hgmjr
     
    Last edited: Sep 20, 2008
  6. bertus

    Administrator

    Apr 5, 2008
    15,650
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    Hello,

    Are you pressing with your fingers to hold the resistor to measure ?
    This can also lead to a lower value.

    Greetings,
    Bertus
     
  7. Musab

    Thread Starter Member

    Sep 20, 2008
    25
    0
    thx

    @bertus why will that happen ?
     
  8. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    resistance of your finger/body in parallel with the measured resistor
     
  9. hgmjr

    Moderator

    Jan 28, 2005
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    214
    The phenomenon being referred to by scubasteve_911 becomes more pronounced as the value of the resistor being measured increases.

    hgmjr
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
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    Perhaps the meter is inaccurate.
     
  11. jtolcou

    New Member

    Nov 1, 2008
    3
    0
    The resisitor should have one leg removed from the circuit and use alligatoe clips when making measurements to eliminate your body's resitance.
     
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