Electromagnetic Induction

Faraday Discovered basic principle of electromagnetic induction Whenever the magnetic field around a conductor is moving or changing magnitude, a current is induced in the conductor

Torus Ring When switch is turned on, a magnetic field is created in coil A and the entire iron ring becomes magnetized Sudden increase in magnetic field causes a current to momentarily be induced in coil B Once the field becomes steady in the ring, induced current no longer exits When switch is turned off, the sudden demagnetization causes current to be again momentarily induced but in opposite direction

Factors Affecting Current Induced Number of loops More loops, greater current Rate of motion of magnetic field Faster motion, greater current Strength of magnetic field Stronger field, greater current

Faraday’s Law Amount of emf induced is proportional to: Rate of change in magnetic field (called flux) Flux is directly proportional to B and A Unit of flux is the Weber (Wb)  = BA cos  Number of loops in the wire Rate of change  = -N (  /t)

Example A conductive wire consisting of 3 loops and enclosing an area of.020 m 2 is perpendicular to a uniform magnetic field of.030T. If the field goes to zero in.0045sec, what is the magnitude of the induced emf?

Example The magnetic flux through a 60 turn coil of wire is reduced from 35Wb to 5.0Wb in.10sec. The average induced current is.0036 A, what is the wire’s resistance?

Direction emf acts in direction opposite to the flux Induced emf gives rise to current whose magnetic field opposes original field

Lenz’s Law Current flows in a direction such that the induced field they create opposes the action of the inducing field Work done moving a magnetic field against its opposing force is transformed into electric energy