(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Hey, How is everyone? I am working on a lab dealing with DC circuits. I am a bit confused about voltmeters and ammeters. We used a carbon composition resistor which obeys Ohm's law and therefore is a linear device. My Paint drawing aren't too pretty but I hope they convey the problem better.

Problem 1:The following circuit was setup:

http://www.utsc.utoronto.ca/~04shaikj/1.bmp

Should the current displayed for both Ammeters be the same?

My Answer 1:Yes, because current is not consumed in a circuit. It's value remain the same throughout the circuit. It is only the electrical energy that is consumed or transformed in the circuit. In the circuit above, the original current (i.e the resistor) has high electrical energy relative to the energy of the current that flows out of the resistor. The resistor converts the electrical energy to heat, dissipating it into the ambient air.

Problem 2:A multimeter set to voltmeter function was used in a position where an ammeter should have been as shown in the circuit below. Is there anything useful displayed on the voltmeter?

http://www.utsc.utoronto.ca/~04shaikj/2.bmp

My Answer 2:Since a voltmeter measures the potential difference across two points, the difference between the power supply and the resistor should equal zero because the current coming out of the power supply has the same electrical energy (ignoring resistance of the wire) as the current going into the resistor. Also, the internal resistance of a voltmeter is high.

Problem 3:A short circuit occured in the electrica circuit below. A multimeter set to ammeter function was used instead of a voltmeter (which should have been used). What happened?

http://www.utsc.utoronto.ca/~04shaikj/3.bmp

My answer 3: What i understand for this question isthat an ammeter is at a position where a voltmeter should have been used. A voltmeter is always hooked up parallel in a circuit to measure the potential difference between two points and it has a large internal resistance so that the correct voltage can be measured. An ammeter is hooked up in series so that all the current goes through it and it has a small internal resistance so that the maximum current can be measured. In the above case, you have the ammeter in parallel instead of series and the current is divided.Umm.. I know about this much but can't seem to answer it.

Problem 4:The resistance (R) of a resistor in a circuit was measured using a voltmeter. It was known that the R of the resistor was a very large value, close to the internal R of the voltmeter. Would you get an accurate measure of R for the resistor?

http://www.utsc.utoronto.ca/~04shaikj/4.bmp

My answer 4: I have no clue for this one. It seems that if the resistor has a huge R value, then the potential difference measured by the voltmeter will be very huge as well. But why would the readings on the voltmeter be inaccurate?... dont know.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Dc Circuits - Voltmeter/ammeter

**Physics Forums | Science Articles, Homework Help, Discussion**