Electromagnetism

Faraday’s Law

The e.m.f. induced is directly proportional to the rate of change of flux linkage

Lenz’s Law

An e.m.f induced by a magnet moving through a coil will always oppose the force that caused it

Cause of magnetic field

Magnetic fields are due to permanent magnets or moving charge

Magnetic flux density practical

Set up a circuit with wire through parallel magnets, set up on a mass balance so that when current flows, there will be downward force. Zero the balance then change variable resistor to change current and record mass. F=BIL. F=mg. Plot F against I. Gradient is equal to B*L therefore divide by L.

Velocity selector

Particles in a velocity selector experience opposing forces from electric and magnetic fields. (opposite and like charges with e fields and LHR with magnetic field). Particles are deflected unless E field and mag field balance where v=E/B. Vary velocity by changing strength of E or B fields.

Electron’s experience a force

When electrons in a conducting for experience a force, (LHR), they accumulate at one end creating a p.d. allowing current to flow.

E.m.f is induced due to

a change in magnetic flux

Faraday’s law to investigate magnetic flux

Place 2 bar magnets opposite, get a search coil (known turns and area), connect it to a data logger, to measure induced e.m.f. with a very small time interval. Place the search coil in the middle of the magnetic field so the area is parallel to the magnets. Start the recorder and move the coil away. e.m.f. is induced due to change in magnetic flux. Data logger plots e.m.f against time. Area under graph of e.m.f against time gives you flux linkage change. (flux linkage = B*A*N) - repeat and mean.

Transformers

A.C. in the primary coil produces an alternating magnetic field. This is passed through the iron core to the secondary coil where it induces an alternating voltage, of the same frequency as input.

Increase transformer efficiency

Lamination reduced eddy currents.

Turns, voltage, current relationship experiment

Step up transformer with voltmeters in parallel. Low voltage from a.c. power. Record V. Then change n ratio between coils and repeat. Add ammeters + variable resistor (to change current) and leave turns the same to investigate equation.