Question

1. In this experiment you will be measuring the resistance of several resistors by measuring the voltage across the resistor and the current through the resistor at the same. When carrying out measurements like this, you always have to be careful that your measuring doesn’t effect the experiment too much, or that if it does, you can correct for it. Current actually passes through both the ammeter and the voltmeter. Each device also has an intrinsic resistance. You may want to check out Section 21.4 of OpenStax, College Physics, to help with this.

   1. (2 pt) Do you expect the voltmeter to have a large or a small internal resistance? Why?

   2. (2 pt) Do you expect the ammeter to have a large or a small internal resistance? Why?

Answer 1

A voltmeter is used to measure the potential difference and is connected in parallel. A voltmeter should not change the amount of current in the circuit. Therefore a voltmeter should have very high internal resistance so that it does not draw any current from the circuit. A ideal voltmeter has infinite internal resistance.

A ammeter is used to measure the electric current and is connected in series. Therefore the correct measurement of current will take place when all the  current will pass through the ammeter . Hence, internal resistance of ammeter should be very low . The internal resistance of ideal ammeter is zero.