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Unformatted text preview: Electromagnetic Induction 1 Induced emf and Magnetic Flux We have seen that electric currents produce magnetic fields. Can magnetic fields produce electric currents? Faradays experiment: (see micro.magnet.fsu.edu/electromag/java/faraday) When the switch is closed or opened, the compass in the second coil shows a brief deflection and then returns to zero. When the switch is opened, the compass deflects in the opposite di- rection and returns then to zero. If there is a constant current in the primary coil, no signal is de- tected. Conclusion: A changing magnetic field produces an electric current in the second coil. The magnetic field created by the electric current is detected by the com- pass. Dr.D.Wackeroth Spring 2005 PHY102A Electromagnetic Induction In order to understand this phenomenon, we need the concept of magnetic flux . Consider a loop of wire in the presence of a uniform magnetic field, ~ B . The loop has an area A . The magnetic flux, is defined as = BA cos (1) where is the angle between ~ B and the normal (perpendicular) to the loop. The SI unit of the magnetic flux is the weber (Wb) : 1 Wb = 1 T m 2 Dr.D.Wackeroth Spring 2005 PHY102A Electromagnetic Induction Remarks: The value of the magnetic flux is proportional to the number of field lines passing through the loop....
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