# Moving Electrical Charges Create Magnetic Field

by Ron Kurtus (revised 23 March 2012)

When an electrical charge is moving or an electric current passes through a wire, a circular magnetic field is created.

This can be seen with iron shavings or filings on a card that will align in the magnetic field when a current is passed through a nearby wire. Using standard conventions for the direction of electric current and magnetic lines of force, the direction of the magnetic can be determined by what is called the right-hand rule for magnetic field. The direction of the magnetic field can be demonstrated by using compasses.

Questions you may have include:

• What happens when electricity goes through a wire?
• What are the electrical and magnetic conventions?
• What is the right-hand rule for current through a wire?

This lesson will answer those questions. Useful tool: Units Conversion

## Magnetic field around wire

When a charged particle—such as an electron, proton or ion—is in motion, magnetic lines of force rotate around the particle. Since electrical current moving through a wire consists of electrons in motion, there is a magnetic field around the wire.

This field can be demonstrated by placing fine iron filings or shavings on a car and sticking a wire through the middle of the card. When a DC electrical current is passed through the wire, the iron filings align to show the magnetic field.

Iron filings show magnetic field around electric wire

## Conventions for electricity and magnetism

Certain conventions are used to determine the direction of the magnetic field with respect to the direction of the current.

### Direction of electrical current

Although electrons have a negative (−) electrical charge and move toward the positive (+) terminal in a wire, the convention is that electrical current moves from positive (+) to negative (−). It is an unfortunate choice that was made years ago, but you need to be aware of the convention.

### Direction of magnetic field

The convention for a magnetic field is that the lines of force move from north (N) to south (S). We don't know if they move in that direction or not, but it is just a convention that everyone follows.

## Right-hand rule for magnetic field

The right-hand rule for determining the direction of the magnetic field is that if you wrapped your right hand around a wire with your thumb pointing in the direction of the electrical current, then your fingers would be in the direction of the magnetic field.

Right-hand rule for electric wire

### Verification with a compass

You can verify the direction of the magnetic field by placing one or more compasses on a card and observing their direction.

Compasses show direction of magnetic field

Note that the current must be DC (direct current), such as from a battery. Otherwise with AC, the direction of the current and magnetic field will alternate 50 or 60 times a second.

## Summary

When electric current passes through a wire, a circular magnetic field is created. Iron filings on a card can demonstrate the magnetic field when current is passed through a nearby wire. Using standard conventions for the direction of electric current and magnetic lines of force, the direction of the magnetic can be determined by what is called the right-hand rule. The direction of the magnetic field can be demonstrated by using compasses.

Learn the basic principles

## Resources and references

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