# Role of a voltmeter in an initially open circuit

• justing943
In summary, when an open circuit is swung through an into page magnetic field, the emf would depend on whether you are asked about the voltage measured between X and Y. The answers can vary between a graph with two spikes or a flat voltage graph. Connecting a volt meter to an open circuit will close the circuit and the amount of impact on the circuit will depend on the properties of the volt meter and the circuit being measured.

#### justing943

Hi!

Could someone briefly explain the following scenario to me please :)

If an open circuit (with the 2 ends named X and Y) hung on a string is swung through an into page magnetic field, what would the emf be? How would that change if you are asked about the voltage 'measured' between X and Y?

The answers that are debatable are between a graph where there are two spikes, one positive one negative, and a completely flat voltage graph.

If an open circuit is connected to a voltmeter (one end to each open end), how would that affect the circuit?

JT

edit: Sorry if this is in the wrong subforum (I suspect it belongs in the HW subforum)

justing943 said:
Hi!

Could someone briefly explain the following scenario to me please :)

If an open circuit (with the 2 ends named X and Y) hung on a string is swung through an into page magnetic field, what would the emf be? How would that change if you are asked about the voltage 'measured' between X and Y?

The answers that are debatable are between a graph where there are two spikes, one positive one negative, and a completely flat voltage graph.

If an open circuit is connected to a voltmeter (one end to each open end), how would that affect the circuit?

JT

edit: Sorry if this is in the wrong subforum (I suspect it belongs in the HW subforum)
Hooking up a volt meter will close the circuit. A volt meter is actually measuring a current through a known impedance, but the scale is tuned into read voltage. However, the current is very low due to the high input impedance of the volt meter. So under "normal" conditions the current that flows through the volt meter is therfor not taken into account. Modern volt meters is controlled by an electronic circuit that has a few million Ohms input impedance.

How much the volt meter affect the circuit will therefor depend on the voltmeter properties and the circuit that is measured.

Vidar

Thanks very much for the reply :). I do believe that solves my problem :D

## 1. What is the purpose of a voltmeter in an initially open circuit?

A voltmeter is used to measure the potential difference between two points in a circuit. In an initially open circuit, a voltmeter helps to determine if there is any potential difference present between the two points.

## 2. How does a voltmeter work in an initially open circuit?

A voltmeter works by connecting it in parallel with the circuit component being measured. In an initially open circuit, the voltmeter completes the circuit and allows the flow of current, which then enables the measurement of potential difference.

## 3. Can a voltmeter be used to measure the current in an initially open circuit?

No, a voltmeter is not designed to measure current. It measures potential difference or voltage. To measure current in an initially open circuit, an ammeter is needed.

## 4. How does a voltmeter affect the circuit in an initially open circuit?

A voltmeter has a very high resistance, so when it is connected in parallel to the circuit, it does not affect the flow of current significantly. However, in a high-precision circuit, the resistance of the voltmeter may cause a small change in the measured potential difference.

## 5. Can a voltmeter be used to measure potential difference in a live circuit?

Yes, a voltmeter can be used to measure potential difference in a live circuit. However, proper precautions must be taken to ensure safety, such as using a voltmeter with appropriate insulation and following proper electrical safety procedures.