Voltmeter question out of TBR physics??

[dray5150]

Could someone please explain why a voltmeter would need to be wired in parallel and have a large internal resistance in order to measure to points along a circuit??


Its question 36 on circuits in TBR

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[kobe200LATE]

So in an ideal voltmeter, all you would want is something that measures the voltage WITHOUT interfering with the rest of the circuit. Therefore, it must be in parallel because if it was in series, it would interfere with the entire circuit. Next, you would want the voltmeter to have a large internal resistance because the higher the resistance, the less current going through the voltmeter. The less current that goes through the voltmeter, the less it would interfere with the actual circuit.

Hope this helps.

 

[dray5150]

That really helped alot. I haven't reviewed resistors in awhile so that really helped. Thanks!!

 

[kobe200LATE]

I actually just went over this passage just now so I have an even better answer for you.

The voltmeter must be in parallel because resistors in parallel have the same voltage so it must be in parallel to get an accurate reading of the voltage. Next, the voltmeter should have a large internal resistance so that the current flowing through it is decreased and its interference with the circuit is minimized.

There was also a similar question in the passage about placing an ammeter to measure the current within the circuit. In this case, you would want to place the ammeter in series because resistors in series have the same current. Next, you would want the ammeter to have a small internal resistance so that it would have a minimal drop in voltage (V decreases and R decreases), keeping the interference from the ammeter minimal.

Hope this helps.