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Module 6 - Chapter 23 - Magnetic fields II - Coggle Diagram
Module 6 - Chapter 23 - Magnetic fields II
Electromagnetic induction
Investigating
Sensetive volemter attached to coil shows no reading when coil and magnet are stationary
Pushing magnet towards coil induces an EMF across the end of the coil, pulling it away reverse the emf
Repeated pushing and pulling induces an ac in the coil
Moving magnet fasts induces greater emf
Explaining
Some of the work done to move the magnet is transferred into electical energy
Motion of the coil relative to the magnetic field makes electrons move because they experience a magnetic force (Bev)
Moving electrons constitute current withint the coil
Magnetic flux
Product of the component of magnetic flux density perpendicular to the area and the cross-sectional area
Unit of magneti flux is the weber (Wb) = 1Tm^2
Magnetic flux linkage - product of number of turns in the coil and the magnetic flux
Emf is induced when there is a change in the magnetic flux linking the circuit
Faraday's law
Magniture of the induced emf is directly proportional to the rate of change of magneitc flux linkage
Relationahip can be written as an equation where the constant of proportionality equals -1
Lenz's law
When you push a magent toward a coil, you do work
Work done no the magnet is equal to the electrical energy produced in the coil
Pushing a north pole towards a coil of wire induces a north pole in the end of the coil closest
Pulling a north pole away from a coil induces a south pole in the end of the coil closes to the north pole
When you push a magnet, the coil end closest can't be a outh pole otherwise energy would be created out of nowhere
Direction of the induced emf/ current is always such as to oppose the change producing it
Alternating current generator
Maximum rate of flux change = greatest induced EMF
As coil rotates, flux linkage changes with time, and can be shown as sinusoidal
Magnitude of gradient from magnetic flux linkeage graph against time equals the induced emf
Induced emf is max wen flux linkage is zero and emg is zero when flux linkage is at a max
Transformers
Transformer - laminated iron core, primary (input) coil and secondary (ouput) coil
alternating current supplied to the primary coil produces a varying magnetic flux in the soft iron core
Iron core ensures all magnetic flux created by the primary coil links the secondary coil and none is lost
Step up transformer - more turns on secondary than primary, Vs > Vp
Step down transformer - more turns on primary than secondary Vs < Vp
Won't work with direct current as there is no changing magnetic flux
Field lines transferred to the secondary coil, where an EMF is inducded from the changing B field
Experimenting
Multimeter set to alternating voltage can be used to measure input and output voltages
Thin copper wires are used to make primary and secondary coils
You can change the number of turns on one or both coils to see what happens to Vs for a fixed Vp
Efficient transformers
Output power of secondary coil equals input power into primary coil
When voltage is stepped up, current is stepped down
Low resistance windings reduces pwoer losses due to heating effects of current
Making a laminated core with layers of iron separated by an insulator helps to minimise currents inducded in the core itself (eddy currents)
Energy is lost through resistive heating in the core, so reducing eddy currents keeps efficiency higher
