electromagnetic induction and faradays law
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Electromagnetic Induction and Faradays Law. Ripon High School AP Physics 2012-2013. Stuff we ’ ll discuss in this unit:. How to induce and emf using a changing magnetic field Faradays Law of Induction Lenz ’ s Law - PowerPoint PPT PresentationTRANSCRIPT
Electromagnetic Induction
and Faradays LawRipon High School
AP Physics 2012-2013
Stuff we’ll discuss in this unit: • How to induce and emf using a changing magnetic field
• Faradays Law of Induction
• Lenz’s Law
• What happens to a conductor moving through a uniform magnetic field
General Information/Questions
• What we know about electricity and magnetism:• An electric current produces a magnetic field• A magnetic field exerts a force on an electric current or
moving electric charge
• QUESTION: If an electric current produces a magnetic field, is it possible that a magnetic field can produce an electric current?
Induced Electromotive Force• Faraday’s Experiment
• Battery• Switch• Iron Ring• Wire• Galvanometer
Induced Electromotive Force• Faraday discovered through his experiment that a
constant current could not induce a current on the other side of the iron ring.
• He did, however, notice that a current was induced on the other side whenever he opened or closed the switch.
• CONCLUSION: • A constant magnetic field does not produce a current in a conductor• A changing magnetic field does produce a current in a conductor
• Induced Current: a current that is induced in a conductor due to a changing magnetic field
Faraday’s Law of Induction
• Further experiments concerning the magnitude of the induced emf led to the following conclusions:• The more rapidly the magnetic field changes, the
greater the induced emf in a loop of wire• Other things the induced emf in a loop of wire
depends upon• The loop’s area• The loop’s angle to the magnetic field
Faraday’s Law of Induction• Magnetic Flux:
• The measure of quantity of magnetism, taking into account the strength and extent of the magnetic field
• Units: Weber [Wb] = [T·m2] Tesla·meter2
• Represented by the Greek letter Phi: Φ• Think of magnetic flux as proportional to the
amount of magnetic field lines passing through a certain area enclosed by the loop
Faraday’s Law of Induction
Faraday’s Law of Induction:
temf B
• ΔΦ – change in flux
• Δt – change in time
Faraday’s Law of Induction
• If the circuit contains a number of loops closely wrapped together, the emfs induced in each wire simply add together (think of a bunch of batteries in series)
tNemf B
• N – number of loops
• ΔΦ – change in flux
• Δt – change in time
Lenz’s Law
• The minus sign prevalent in Faraday’s Law reminds us the direction the induced emfs act, summed up by Lenz’s Law:
A current produced by an induced emf moves in a direction so that its magnetic field opposes the original
change in flux
Lenz’s Law• TWO MAGNETIC FIELDS EXIST!
• The changing magnetic field or flux that induces the current
• The magnetic field produced by the induced current
• Important Rule: The second magnetic field opposes the change in the first
Induced emf in a Moving Conductor• Another way to induce an emf in a conductor is to
move it through a magnetic field.
• For our purposes, you must assume:• The conductor has some length• The conductor has some velocity • The magnetic field is uniform• All three are perpendicular to one another
emf Induced in a Moving Conductor• In order to calculate the induced emf in a conductor,
the following equation applies:
Blvemf • B – magnetic field• l – length of conductor• v – velocity of conductor