# Need help with simple circuits

Discussion in 'Homework Help' started by richardsim10, Sep 10, 2008.

1. ### richardsim10 Thread Starter New Member

Sep 10, 2008
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Ok so I'm at my 12th year of school and I have this lab that I didn't really understand. I have 3 questions to answer and I don't have any clue on this. They are asking me How a voltmeter and ammeter should be connected in a circuit so that the circuit, within experimental range, remains unchanged and explain why it does not affect the circuit when properly connected? Other question is that how the voltages changes follow Kirchoff's loop rule.
Now I'm only doing simple circuits in series, so it's not something complicated. Basically we were dealing with a power supply, 2 resistors and 1 ammeter and voltmeter.
Thanks for taking the time to answer and help me out.

2. ### beenthere Retired Moderator

Apr 20, 2004
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295
Ammeters and voltmeters have stated resistances, so the affect they will have on the circuit can be calculated. There is no special way to use/connect a meter such that it will have less influence on the measured circuit. The voltmeter measures in parallel, the ammeter goes in series with the circuit elements.

Here is the explanation of KVL in our Ebook - http://www.allaboutcircuits.com/vol_1/chpt_6/2.html. Easy to see in a series circuit.

Sep 10, 2008
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Ok thx a lot

4. ### cwilli85 New Member

Sep 10, 2008
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I believe the answer to the question that you're trying to answer is that they have no effect on the circuit because the ameter, being connected in the circuit so that the current flows through it, idealy has no resistance. Although the meter actually has some internal resistance it is usually for, classroom purposes, treated as a neglegable resistance, so it can be ignored, thus not effecting the circuit.
The voltmeter on the other had is connected in parallel to measure the voltage "drop". The voltmeter is modeled has having infinite resistance, thus looking like an open in the circuit so no current flows through it. although a small amount of current actually does flow, it is usually ignored in lower lever electrical classes.

5. ### richardsim10 Thread Starter New Member

Sep 10, 2008
3
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ok cool thx a lot, I had an idea similar to that with all the results, but i couldnt figure our because of some stuffs that went wrong during the experiment