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 m2 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