# Magnetic field and wire

Magnetic field created by a current Video transcript Let's explore the repercussions of this equation some more. So what was the equation? It was that the force of a magnetic field on a moving charged particle is equal to the charge-- that's not what I wanted to do-- is equal to the charge of the particle-- and that's just a scalar quantity-- times the velocity-- the cross product of the velocity of the particle-- with the magnetic field. Now, isn't the velocity vector just the same thing as the distance vector divided by time?

The vector B is termed the magnetic field, and it is defined as the vector field necessary to make the Lorentz force law correctly describe the motion of a charged particle. This definition allows the determination of B in the following way [14] [T]he command, "Measure the direction and magnitude of the vector B at such and such a place," calls for the following operations: Take a particle of known charge q.

Measure the force on q at rest, to determine E. Then Magnetic field and wire the force on the particle when its velocity is v; repeat with v in some other direction. Now find a B that makes the Lorentz force law fit all these results—that is the magnetic field at the place in question.

Alternatively, the magnetic field can be defined in terms of the torque it produces on a magnetic dipole see magnetic torque on permanent magnets below.

Alternative names for H [13] [15] Magnetic field intensity Magnetic field Magnetizing field In addition to B, there is a quantity H, which is often called the magnetic field. Inside a material they are different see H and B inside and outside magnetic materials.

The term "magnetic field" is historically reserved for H while using other terms for B. Units[ edit ] In SI units, B is measured in teslas symbol: Devices used to measure the local magnetic field are called magnetometers. Important classes of magnetometers include using induction magnetometer or search-coil magnetometer which measure only varying magnetic field, rotating coil magnetometerHall effect magnetometers, NMR magnetometersSQUID magnetometersand fluxgate magnetometers.

The magnetic fields of distant astronomical objects are measured through their effects on local charged particles. For instance, electrons spiraling around a field line produce synchrotron radiation that is detectable in radio waves.

Magnetic field lines[ edit ] Main article: Field line The direction of magnetic field lines represented by iron filings sprinkled on paper placed above a bar magnet.

Mapping the magnetic field of an object is simple in principle. First, measure the strength and direction of the magnetic field at a large number of locations or at every point in space. Then, mark each location with an arrow called a vector pointing in the direction of the local magnetic field with its magnitude proportional to the strength of the magnetic field.

The direction of the magnetic field at any point is parallel to the direction of nearby field lines, and the local density of field lines can be made proportional to its strength. Magnetic field lines are like streamlines in fluid flowin that they represent something continuous, and a different resolution would show more or fewer lines.

For example, the number of field lines through a given surface is the surface integral of the magnetic field.

Various phenomena have the effect of "displaying" magnetic field lines as though the field lines were physical phenomena. Field lines can be used as a qualitative tool to visualize magnetic forces. In ferromagnetic substances like iron and in plasmas, magnetic forces can be understood by imagining that the field lines exert a tensionlike a rubber band along their length, and a pressure perpendicular to their length on neighboring field lines.

The rigorous form of this concept is the electromagnetic stress—energy tensor. Magnetic field and permanent magnets[ edit ] Main article: 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 - Wikipedia

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 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.

## Magnets and Magnetic Force

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.A long straight wire carrying a current has a magnetic field due to moving charges which will depend on the right-hand rule.

For the case of a long straight wire carrying a current I, the magnetic field lines wrap around the wire and depends on the distance to the wire.

The magnetic field of an infinitely long straight wire can be obtained by applying Ampere's metin2sell.com's law takes the form.

## Electromagnet - Wikipedia

and for a circular path centered on the wire, the magnetic field is everywhere parallel to the path. The fingers show the direction of the magnetic field which wraps around the wire. [Explain] The right-hand-grip-rule is a useful shortcut, but does have a more fundamental origin as the vector cross product.

The magnetic field lines around an electrified wire form concentric circles around the wire. The direction of the magnetic field is perpendicular to the wire and is in the direction the fingers of your right hand would curl if you wrapped them around the wire with your thumb pointing in the direction of the current.

The magnetic field is strongest in the area closest to the wire, and its direction depends upon the direction of the current that produces the field, as illustrated in this applet.

Presented in the tutorial is a straight wire with a current flowing through it. Magnet Wire | PowerwerxDesign Your Own · Portable Power · Digital Display · Need Help.

What are magnetic fields? (article) | Khan Academy