Back to IB Physics > 12 Electromagnetic Induction

12.1 INDUCED ELECTROMOTIVE FORCE

MOST OF THESE IDEAS ARE DEMONSTRATED BY THE PHET FARADAY SIMULATION also known as Generator Simulation

Describe the inducing of an emf by relative motion between a conductor and a magnetic field.

ELECTROMAGNETIC INDUCTION: An emf is induced when the magnetic field passing through an electric conductor changes. An induced current flows when the conductor is in a circuit.

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Derive the formula for the emf induced in a straight conductor moving in a magnetic field.
Students should be able to derive the expression induced emf = Blv without using Faraday’s law.
E=Bvl.png
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An electron in the bar of length L, experiences a force (=Bev) due to its motion in a magnetic field and moves. The displaced electrons exert an electric force (=Ee) in the opposite direction. An equilibrium will be achieved and the forces will balance (Bv=E). The electric field E= the potential gradient =V/L, so Induced emf = BLv.

Define magnetic flux and magnetic flux linkage.

MAGNETIC FLUX DENSITY, B: The strength of the magnetic field. The force acting on a conductor per unit current length. Unit: 1 tesla (T) = 1 NA^-1m^-1
MAGNETIC FIELD LINES: The density of the lines in an area is proportional to the strength of the field. The lines ‘thread’ or ‘link’ the coil. When the coil moves relatively to the field, the lines may ‘cut’ the coil.
MAGNETIC FLUX, Φ: The magnetic flux through a small plane surface is the product of the flux density normal to the surface and the area of the surface.
Φ=BA where B is the flux density acting at right angles to the surface and A is the area of the surface. Unit: 1Tm^2 = 1 weber (Wb)
MAGNETIC FLUX LINKAGE: The flux linkage through a coil of N turns is NΦ
If the B-field is at an angle θ to the normal,
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Describe the production of an induced emf by a time-changing magnetic flux.

Instead of the moving magnet, an emf will be induced by a magnetic field changing over time.

State Faraday’s law and Lenz’s law.

FARADAY’S LAW: The induced emf is directly proportional to the rate of change of flux linkage or rate of flux cutting
Faraday_law_formula.png
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LENZ’S LAW: The direction of the induced emf is such that it tends to oppose the flux change causing it, and does oppose it if the induced current flows.

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Solve electromagnetic induction problems.