# Relationship of electric currents and magnetic fields

### Relation between electricity and magnetism

Magnetic field lines form in concentric current I (a constant flow of electric. Biot-Savart Law: An equation that describes the magnetic field generated by an electric current. It relates the magnetic field to the magnitude, direction, length. Electric current flowing through a single loop of wire does not generate a very powerful magnetic field. A coil of wire looped many times makes.

Magnet Permanent magnets are objects that produce their own persistent magnetic fields. They are made of ferromagnetic materials, such as iron and nickelthat have been magnetized, and they have both a north and a south pole. Magnetic field of permanent magnets[ edit ] Main articles: Magnetic moment and Two definitions of moment The magnetic field of permanent magnets can be quite complicated, especially near the magnet.

The magnetic field of a small [nb 7] straight magnet is proportional to the magnet's strength called its magnetic dipole moment m. The equations are non-trivial and also depend on the distance from the magnet and the orientation of the magnet.

For simple magnets, m points in the direction of a line drawn from the south to the north pole of the magnet. Flipping a bar magnet is equivalent to rotating its m by degrees. The magnetic field of larger magnets can be obtained by modeling them as a collection of a large number of small magnets called dipoles each having their own m. The magnetic field produced by the magnet then is the net magnetic field of these dipoles.

And, any net force on the magnet is a result of adding up the forces on the individual dipoles. There are two competing models for the nature of these dipoles.

These two models produce two different magnetic fields, H and B. Outside a material, though, the two are identical to a multiplicative constant so that in many cases the distinction can be ignored. This is particularly true for magnetic fields, such as those due to electric currents, that are not generated by magnetic materials. Magnetic pole model and the H-field[ edit ] The magnetic pole model: It is sometimes useful to model the force and torques between two magnets as due to magnetic poles repelling or attracting each other in the same manner as the Coulomb force between electric charges.

This is called the Gilbert model of magnetism, after William Gilbert. In this model, a magnetic H-field is produced by magnetic charges that are 'smeared' around each pole. These magnetic charges are in fact related to the magnetization field M.

• Magnetic Fields and Electric Current

The H-field, therefore, is analogous to the electric field E, which starts at a positive electric charge and ends at a negative electric charge.

Near the north pole, therefore, all H-field lines point away from the north pole whether inside the magnet or out while near the south pole all H-field lines point toward the south pole whether inside the magnet or out. Too, a north pole feels a force in the direction of the H-field while the force on the south pole is opposite to the H-field. The magnetic pole model predicts correctly the field H both inside and outside magnetic materials, in particular the fact that H is opposite to the magnetization field M inside a permanent magnet.

Since it is based on the fictitious idea of a magnetic charge density, the Gilbert model has limitations.

### electromagnetism - Magnetic Field and Current Relationship - Physics Stack Exchange

If a magnetized object is divided in half, a new pole appears on the surface of each piece, so each has a pair of complementary poles. The magnetic pole model does not account for magnetism that is produced by electric currents. Amperian loop model and the B-field[ edit ] See also: Gauss's law for magnetism The Amperian loop model: A current loop ring that goes into the page at the x and comes out at the dot produces a B-field lines. The north pole is to the right and the south to the left.

In this model developed by Ampere, the elementary magnetic dipole that makes up all magnets is a sufficiently small Amperian loop of current I.

### Relationship Between Electricity & Magnetism | Sciencing

These magnetic dipoles produce a magnetic B-field. One important property of the B-field produced this way is that magnetic B-field lines neither start nor end mathematically, B is a solenoidal vector field ; a field line either extends to infinity or wraps around to form a closed curve. See magnetic monopole below. Magnetic field lines exit a magnet near its north pole and enter near its south pole, but inside the magnet B-field lines continue through the magnet from the south pole back to the north.

In the similar way, the flow of electricity or charged particles especially free electrons in a particular direction is called current electricity or electric current. Magnetism is a type of attractive or repulsive force that acts up to certain distance. The distance up to which this attractive or repulsive force acts is called magnetic field. Magnetism is caused by the moving electric charges especially electrons.

When two magnetic materials are placed close to each other, they experience an attractive or repulsive force. We know that all the objects in the universe are made of small particles called atoms. The atoms consist of sub atomic particles such as electrons, protons, and neutrons.

## Magnetic Field Basics

The strong nuclear force between the protons and neutrons makes them stick together to form nucleus. The electrons present in the atom revolve around the nucleus because of the electrostatic force of attraction between the electrons and nucleus.

The electrons revolving around the nucleus also rotates or spins around its own axis. Because of this spinning of electrons, magnetic field is produced.

If the majority number of electrons in the atom spins in the same direction, a strong magnetic field is produced. The direction of the electrons spin determines the direction of magnetic field.

On the other hand, if the equal number of electrons in the atom spins in the opposite direction, the spinning speed of the electrons cancels out. Thus, the magnetism also cancels out. Relationship between electricity and magnetism In the early days scientists believed that, electricity and magnetism are two separate forces.