Electromagnetic Induction AP Physics Chapter 21

Electromagnetic Induction 21.1 Induced EMF

Induced EMF Michael Faraday – a changing magnetic field can produce an electric current This is an induced current 21.1

Induced EMF A magnet moved quickly into a coil of wire induces a current When it is quickly moved the other way, a current is induced in the opposite direction 21.1

Electromagnetic Induction 21.2 Faraday’s Law of Induction; Lenz’s Law

Faraday’s Law of Induction; Lenz’s Law From experiments the induced emf depends on 1.Rate of change of the magnetic field 2.Loop’s area 3.Angle Magnetic flux is the total number of magnetic field line passing through the are enclosed by the loop 21.2

Faraday’s Law of Induction; Lenz’s Law Magnetic Flux When  is 90, no field lines pass through the loop The unit for magnetic flux is a weber 21.2

Faraday’s Law of Induction; Lenz’s Law Since the induced EMF is the rate of change of flux This is Faraday’s Law of Induction For multiple loops in a magnetic field Where N is the number of loops in the field 21.2

Faraday’s Law of Induction; Lenz’s Law Lenz’s Law – a current produced by an induced emf moves in a direction so that its magnetic field (produced by the current) opposes the original change in flux 21.2

Faraday’s Law of Induction; Lenz’s Law Steps in problem solving – Lenz’s Law 1.Determine if the magnetic flux inside the loop is decreasing, increasing, or unchanged 2.The magnetic field due to the induced current a. Points in the same direction as the external field if the flux is decreasing b. Points in the opposite direction if the flux is increasing c. Is zero if the flux is not changing 21.2

Faraday’s Law of Induction; Lenz’s Law Steps in problem solving – Lenz’s Law 3.Use the right hand rule-1 to find the direction of the induced current 4.Always keep in mind that there are two magnetic fields a. An external field whose flux must be changed if it is to induce an electric current b. A magnetic field produced by the induced current 21.2

Electromagnetic Induction 21.3 EMF Induced in a Moving Conductor

Faraday’s Law of Induction; Lenz’s Law If the rod above is made to move at a velocity v The area of the rod increases So the change in area is The induce EMF is 21.3

Faraday’s Law of Induction; Lenz’s Law Sometimes called motional emf True as long as components are mutually perpendicular 21.3

Electromagnetic Induction 21.4 Changing Magnetic Flux Produces an Electric Field

Changing Magnetic Flux Produces Electric Field Since there is an induced current when there is an induced EMF, there must be an electric field A changing magnetic field induces an electric field So since And The electric field must be 21.4

Electromagnetic Induction 21.5 Electric Generators

Electric Generators Generator – converts mechanical energy (spinning) into AC current. If we look at just one perpendicular arm of the loop Since we have two arms in each loop Now if we add loops 21.5 Generator Simulation