ELECTRO MAGNETIC INDUCTION ANDREW MOAKES

ELECTRO MAGNETIC INDUCTION ANDREW MOAKES

1. VOLTAGE INDUCTION

   • Voltage is induced across a wire when it cuts through a magnetic field
   • the wire cuts through the field lines up and down

2. electromagnetic induction

   • The EMF (electromotive force) or voltage induced across a conductor is directly proportional to the rate at which the field lines are cut V∝ NUMBER OF FIELD LINES CUT PER SECOND
   • Flemings right hand rule
     • this is used for a wire moving through a magnetic field. thuMb=motion First finger=field seCond finger=current
   • Rotating the coil twice as fast = 2xAmplitude and 2xNumber of oscillations

3. AC generator

   • As the coil spins the wires on the side of the coil cut the magnetic field lines. The induced voltage drives a current which flows through slip rings which press against carbon brushes. As the generator spins round, the current in the circuit change direction. Hence the name alternating current generator.
   • To increase the voltage 1)More turns of wire on coil. 2) stronger magnet 3) Larger area of coil 4) Faster speed of movement

4. TRANSFORMERS

   • A transformer is used to change the voltage of an AC SUPPLY
   • transformer equation: Vp/Vs = Np/Ns V is voltage N is number of turns P is primary and S is secondary
   • Step up transformers increase voltage Ns is bigger than Np
   • Step down transformers decrease voltage Np is bigger than Ns
   • 1) An alternating current flows through the transformer. 2)This creates a changing magnetic field in the iron core 3)the changing magnetic field is cut by the secondary coil. 4)This induces a voltage across the secondary coil 5)This is an alternating voltage to the changing direction of the magnetic field 6) The size of the induced voltagedepends onthe ratio of number of turns of each coil
   • Transformer efficiency Use thicker wire or use a laminated core making it more difficultfor current to flow in the coil.

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