2.6 concepts - magnetic fields and electromagnetic induction

Investigation of force of a wire

The current is varied, and the change in weight of the magnets is recorded - the change in weight is due to the force of the magnetic field generated by the wire

Alternating current generator

As a wire moves through a magnetic field, the wire cuts magentic field lines, inducing an emf. There is induced emf in a coil that is rotating uniformly with angular rotation in a magnetic field.

Positive FBv

Left hand FBI = FBv

Negative FBv

Left hand FBI = FBv (force in opposite direction)

Charges moving in circular paths

If it occurs in the presence of a magnetic field, we know that the force acting on the particle must be acting towards the centre of the circle. The magnetic field is being used to control the path direction of the moving charge. This concept is used in devices such as cyclotrons used in medical machinery to provide radiotherapy treatment.

Alternating currents

The power deliver to homes and businesses. It’s easier to use root mean square currents and voltages, rather than discussing power supplies as functions.

Transformers

used in the national grid to transmit electricity at high voltages and low current to reduce the power loss in cables

Use of a core in a transformer

Increase the linkage of magnetic flux between the primary coil and the secondary coil, by providing a path with a high magnetic permeability.

Causes of inefficiency in transformers

Resistance in the cells, eddy currents, work done to produce magnetic field

Efficiency improvements

Lamination reduces energy losses as heat, as the core is constructed from thin sheets of iron separated by an insulating material with high resistivity, which reduces and limits the flow of eddy currents.

magnetic flux and angle relationship in a rotating coil

inverse relationship, inducing an emf

Investigating magnetic fields

A search coil can be used, as the coil moves through a magnetic field, an emf is generated, which can be measured