Topic 4c: magnetism

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Magnetism: a property of matter

For a standard bar magnet with poles, the field is attractive for opposite poles and repulsive for like poles.

All magnets have 2 poles; the North and South poles always exist in pairs, so if a permanent magnet is split in 2, there would be 2 smaller magnets generated, each having their own North and South poles.

Magnetic field: an attractive or repulsive force field generated by a moving charged particle.

field lines are used to represent magnetic forces

The direction of magnetic field is tangent to the field line at any point in space.

Magnetic field lines can never cross one another.

The strength of the magnetic field is proportional to the closeness of the lines.

Magnetic field lines are continuous, forming closed loops without beginning or end. They go from the North Pole to the South Pole.

The North and South poles cannot be separated. This is distinctly different from electric field lines, which begin on the positive and end on the negative.

A vector quantity expressed in units of tesla (T) and/or gauss (G), with the latter more commonly used for smaller magnetic fields.

1 tesla = 1 newton/ampere*meter = 1 weber/meter^2

1 T = 1 × 10^4 G.

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Created in the presence of moving charges or current; magnitude and direction of magnetic field is determined by the behavior of the current that creates it.

particles in the magnetic field move in a cyclical or helical pattern; thus the magnetic field does no net work.

4 configurations of current are commonly used to identify the magnitude of magnetic field in those situations; direction is determined using the right hand rule.

Magnetic force: force exerted on a charge/current moving in a uniform magnetic field.

Direction of the magnetic force can be determined using the right hand rule

thumb points in the direction of the motion of the charge. Rest of the fingers follow the magnetic field lines. Palm will face the direction of the magnetic force.

Magnetic force on a charged particle

F = qvB sinθ

F= magnetic force

q= charge of particle

v= velocity of particle

B= magnitude of magnetic field

θ= angle between direction of velocity and lines of magnetic field

Magnetic force exerted on a current carrying wire placed in a uniform magnetic field is -->

F = ILB sinθ

F= magnetic force

I= magnitude of current

L= length of wire

B= magnitude of magnetic field

θ= angle between direction of current and lines of magnetic field

Lorentz Force: combined force on a charged particle due to both electric and magnetic fields