Measurements with an Ammeter/Voltmeter

[jumbogala]

Homework Statement

1) What is needed for an ammeter to measure current accurately?
2) What is needed for a voltmeter to measure the potential differences in the circuit accurately?

3) How can you construct an ammeter from a resistor and a galvanometer?
4) How can you construct a voltmeter from a resistor and a galvanometer?

Homework Equations

The Attempt at a Solution

For 1 & 2, I just want to make sure I’m not missing any major reasons. An ammeter should have a resistance as close to 0 as possible and should be connected in series. A voltmeter has a theoretical resistance of infinity and should be connected in parallel.

3 & 4 have me confused... I thought a galvanometer was equivalent to an ammeter! Can you just pick a galvanometer with the appropriate resistance and hook it up properly?

 

[ehild]

A galvanometer can measure very low current and voltage values, in the range of micro amps and millivolts. If you want to measure higher current and voltage, you have to extend the range of the galvanometer, by ensuring that no higher than the allowed current flows through it. By connecting a resistor parallel with the galvanometer, part of the current will flow through this parallel resistor, called shunt. f you want to measure voltage, you need to connect a resistor in series with the galvanometer so as part of the voltage should drop across this multiplier.

ehild

 

[kerimek]

I can confirm that your understanding for the requirements of an ammeter and voltmeter are correct. An ammeter should have a very low resistance, close to 0, in order to minimize its impact on the circuit and accurately measure the current flowing through it. It should also be connected in series with the circuit to ensure that all the current passes through it. On the other hand, a voltmeter should have a very high resistance, ideally infinity, in order to minimize the current flowing through it and accurately measure the potential difference in the circuit. It should be connected in parallel to the circuit to measure the voltage across the component of interest.

Regarding constructing an ammeter and voltmeter from a resistor and a galvanometer, it is possible to do so. A galvanometer is a device that is used to measure small currents, and it can be calibrated to read these currents in amperes. So, by adding a low resistance resistor in series with the galvanometer, we can create an ammeter. The current will flow through the galvanometer and the resistor, and the reading on the galvanometer will give us the value of the current passing through the circuit.

Similarly, to create a voltmeter, a high resistance resistor is added in parallel with the galvanometer. This will cause most of the current to flow through the resistor, and the remaining small current will pass through the galvanometer, giving us a reading of the potential difference across the component in the circuit.

It is important to note that the resistances of the galvanometer and the added resistors should be carefully chosen to ensure accurate measurements and to prevent damage to the circuit. Additionally, the construction of these makeshift instruments may not be as precise as commercially available ammeters and voltmeters, so their readings may have some degree of error.