(22) Electromagnetic Induction

(22) Electromagnetic Induction - Lecture Notes 22...

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Electromagnetic Induction Lecture Notes 22
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Goals To overview electromagnetic induction and Faraday’s Law. To observe examples of Lenz’s Law. To study motional electromotive force. To understand eddy currents. To study and calculate mutual and self inductance. To understand and calculate the action of transformers. To study and calculate magnetic field energy. To study R-L and L-C circuits.
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Induction Experiments Does the field induce a current or not? Induced emf and induced current “relative motion” of the magnet and coil induces emf and current in the coil circuit. If the coil circuit were open, there would be no induced current. However, an emf would still be induced in the coil, whether the current exists or not. The phenomenon of producing an induced emf with the aid of a magnetic field is called electromagnetic induction.
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22.1 Induced Emf and Induced Current The current in the coil is called the induced current because it is brought about by a changing magnetic field. Since a source emf is always needed to produce a current, the coil behaves as if it were a source of emf. This emf is known as the induced emf. There are a number of ways a magnetic field can be used to generate an electric current. A changing magnetic field induces an emf in the coil, and the emf leads to an induced current.
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± While the area of the coil is changing, an induced emf and current are generated ± An emf can be induced by changing the area of a coil in a constant magnetic field ± I ne a c he x am p l e ,b o t ha nem f and a current are induced because the coil is part of a complete circuit. If the circuit were open, there would be no induced current, but there would be an induced emf.
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When a conducting rod moves at right angles to a constant magnetic field, the magnetic field causes opposite charges to appear at the ends of the rod, giving rise to an induced emf. The induced emf causes an induced current I to appear in the circuit. Motional emf is the emf which originates from the motion of charges through a magnetic field. 22.2 Motional Emf
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The electric force F e = Eq = ( / L ) q and magnetic force F B = qvB balance at equilibrium. The emf, then, is: Motional emf when v , B , and L are mutually perpendicular E = vBL As expected, = 0 V when v = 0 m/s, for no motional emf is developed in a stationary rod.
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22.2 Motional Emf Example 1 Operating a Light Bulb with Motional Emf Suppose the rod is moving with a speed of 5.0m/s perpendicular to a 0.80-T magnetic field. The rod has a length of 1.6 m and a negligible electrical resistance. The rails also have a negligible electrical resistance. The light bulb has a resistance of 96 ohms. Find (a) the emf produced by the rod and (b) the current induced in the circuit. (a) () ( ) ( ) V 4 . 6 m 6 . 1 T 80 . 0 s m 0 . 5 = = = vBL E A 067 . 0
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This note was uploaded on 04/01/2011 for the course PHY 135 taught by Professor Wagihghobriel during the Spring '11 term at University of Toronto- Toronto.

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(22) Electromagnetic Induction - Lecture Notes 22...

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