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Homework Help: Ammeter and voltmeter confusionhelp please

  1. Nov 28, 2006 #1
    i know why an ammeter is always in series with the resistor(s)
    but i don't know why a voltmeter is in parallel with the resistor(s)
    can somebody explain this?

    thank you:D
  2. jcsd
  3. Nov 28, 2006 #2


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    If you put a voltmeter in series in a circuit, what voltage would it be measuring? When used in the usual way, you want the meter to not affect the circuit, but it always does have some effect.
  4. Nov 28, 2006 #3
    In order to understand this you have to think about what each meter is measuring. I'll assume you know and understand what the ammeter is measuring, so we won't go over that.

    The voltmeter, of course, measures voltage. If you remember back to your first physics class, voltage was defined as a potential difference between two points in space. Notice the word "difference." This implies that you need two distinct points in space at two distinct potentials in order to measure a potential difference between them, or a voltage. Voltages are never absolute, they are always measured with respect to something. If you were to hook up a voltmeter in series with a circuit component, you would read zero. This is because you've essentially connected your voltmeter in parallel to one point in the circuit. There can be no potential difference if there is no difference in space.

    I hope that helps.
  5. Feb 7, 2010 #4
    The Voltmeter is a very high resistance device....if connected in series, it blocks the main current in the circuit completely (resistance in series is greater than resistance when connected in parallel). So when the voltmeter is connected in parallel, only 1/(device resistance) is introduced into the circuit....................... which is almost next to zero.
    I hope this helped
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