Magnetism Flashcards
Magnetic Flux
measured in webers (Wb)
the total magnetic field that passes through a given area
Φ = BA
Magnetic Flux Density
The force acting per unit current per unit length on a current-carrying conductor placed perpendicular to the magnetic field
measured in teslas
B = F/IL
Magnetic Flux Linkage
The product of the magnetic flux and the number of turns
ΦN = BAN
units of Weber turns (Wb turns)
Faraday’s Law
the magnitude of the induced emf is directly proportional to the rate of change of magnetic flux linkage.
Lenz’s Law
the direction of the induced emf or current is always such as to oppose the change producing it.
when is an emf induced
when there is a change in the magnetic flux linking the circuit.
Faradays law equation
-nphi/t
whats the most efficient transfer of energy
high transmission voltage, low transmission current
when is force strongest
when the wire is perpendicular to the field
why does a current carrying wire experience a force
each eelctron moving inside the wire experiences a tiny force
what happens when a magnet enters a coil
an emf is induced across the ends of the coil, and when the magnet is pulled away a reverse emf is induced, this induces an ac current .
how do transformers work
ac current is supplied to the primary coil which produces a varying magnetic flux in the soft iron core. secondary coil is linked by the changing dlux, and according to faraday’s law a varying emf is produced across th ends of the secondary coil.
voltage and current in a step up transformer
voltage is stepped up but current is stepped down
how to reduce eddy currents in an iron core
laminate
why is core made from soft iron
its easy to magentise and demagnetise
