The Magnetic Field

Properties of Magnets

Magnetic field strength is given the symbol H with the unit Tesla

Magnetic flux density is given the symbol B and has the unit (W m^-2) To measure the magnetic field caused by a current the Biot Savart law is used.

The magnetic field is a vector field which means that it has a magnitude and direction for each point in space. The strength and direction of the magnetic field at any point is defined in terms of the force on a moving charged particle such as an electron. The force created the magnetic field comes from the Lorentz equation without the electric field. by measuring the force on a unit test charge. The magnetude and direction come from the Lorentz force equation.

F = q (v x B)

Since we are dealing with a cross-product, the direction of the force is a direction perpendicular to the plane of v and B. and the magnitude of the force is then F= q v B sin θwhere theta is the angle between B and v.

A magnetic field is the lines of force generated by a magnetic. Since a magnetic monopole has never been found, it does not make sense to talk about a magnetic point charge. Instead, lines of magnetic field form closed loops along line of equal magnetic force. The strength of the magnetic field is determined by the number of field lines passing a unit area. The more field lines the stronger the magnetic field. A unit of magnetic field strength is known as the Gauss is defined as one magnetic field line per square centimetre. The direction of the field line could be determined by using a compass needle. Its direction creates a tangent line to the magnetic field at that point.

By convention the arrow tip on magnetic field lines points towards the south magnetic pole and away from the north magnetic pole. The magnetic poles alway occur in pairs, no one has ever found a magnetic monopole, though there is research into their posible existance.

The image shows the field lines produced by a bar magnet. Iron fillings are sprinked on a piece of paper and the bar-magnet is placed under the paper. The iron-fillings line up and show the intensity of the magnetic field.