# Magnetic fields

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A magnetic field is a region in which a particle with magnetic properties experiences a force, and in which a moving particle experiences a force.

Magnetic flux is the flow of field lines. (units Wb)

There are two types of magnets: Permanent, and electro.

Permanent magnets:

The fields lines ALWAYS go from north to south.

The arrows represent the direction of the force that a free north pole would experience.

The closer the lines are, the stronger the magnetic field.

Electromagnets:

The cross in the centre of the wire shows the wire is going away from us.

Direction of field: into page- clockwise, out of page- anticlockwise

Where to magnets coincide and cancel each other out, it is called a neutral point.

Magnetic Field Strength (B)

Aka: mangetic flux density. (units T)

Flux density is dependent on the amount of flux and the angle of the area (often a coil) to the field.

1 T = 1 Wb/m²

1 T is VERY BIG. a strong permanent magnet is about 0.1 T

A magnetic field has a strength of 1T if a wire of length 1 metre experiences a force of 1N when a current of 1A flows in the wire.

Force on a wire generating a current = BIL

The direction of the force is given by Fleming's left hand rule:

A couple on a coil.

Torque (C) on the coil = Fa sinθ = BNIba sin θ   or:

Torque (C) on the coil = BANI sinθ

Treat this as a moments question.

Moving Charges

Diriving the equation for moving charges.

F = BIL I =…

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