# Measurements with an Ammeter/Voltmeter

• jumbogala
In summary: The key to accurately measuring current with an ammeter is to have a resistance as close to 0 as possible and to connect it in series with the circuit. For a voltmeter, the key is to have a theoretical resistance of infinity and to connect it in parallel with the circuit. To construct an ammeter or voltmeter from a galvanometer, you need to add a resistor in either series or parallel to extend the range of the galvanometer. This resistor, also known as a shunt or multiplier, will allow for the measurement of higher currents or voltages.
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?

## 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?

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

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.

## What is an ammeter and how does it measure electric current?

An ammeter is an instrument used to measure the flow of electric current in a circuit. It typically consists of a needle or digital display that indicates the amount of current passing through the circuit. To measure current, the ammeter must be connected in series with the circuit, meaning it is placed in the path of the current flow.

## What is a voltmeter and how does it measure electric potential difference?

A voltmeter is an instrument used to measure the electric potential difference, also known as voltage, between two points in an electrical circuit. It works by measuring the amount of electrical energy required to move a small amount of charge from one point to another. To measure voltage, the voltmeter must be connected in parallel with the circuit, meaning it is placed across the component or points where the potential difference is to be measured.

## What is the difference between an ammeter and a voltmeter?

An ammeter measures electric current while a voltmeter measures electric potential difference. Ammeters are connected in series with the circuit, while voltmeters are connected in parallel. Additionally, ammeters have a lower resistance compared to voltmeters, as they need to allow current to flow through them, while voltmeters have a higher resistance to prevent excess current from passing through.

## How do I use an ammeter and voltmeter to measure resistance?

To measure resistance, the ammeter and voltmeter must be connected in a circuit which contains the component whose resistance is to be measured. The ammeter should be connected in series and the voltmeter in parallel with the component. The resistance can then be calculated using Ohm's law (R = V/I), where V is the voltage measured by the voltmeter and I is the current measured by the ammeter.

## What factors can affect the accuracy of measurements with an ammeter and voltmeter?

The accuracy of measurements with an ammeter and voltmeter can be affected by various factors such as the accuracy of the instruments themselves, the resistance of the wires used to connect the instruments, and the internal resistance of the circuit components. Additionally, external factors such as temperature and humidity can also affect the accuracy of measurements.

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