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Transcript

Chapter 31 Faraday’s Law CHAPTER OUTLINE 31.1 Faraday’s Law of Induction 31.2 Motional emf 31.1 Faraday’s Law of Induction The total induced emf in the coil is given by the expression Suppose that a loop enclosing an area A lies in a uniform magnetic field B, as in Figure . The magnetic flux through the loop is equal to BA cos # ; hence, the induced emf can be expressed as: Example 31.1 One Way to Induce an emf in a Coil 31.2 Motional emf we considered cases in which an emf is induced in a stationary circuit placed in a magnetic field when the field changes with time. In this section we describe what is called motional emf, which is the emf induced in a conductor moving through a constant magnetic field. The condition for equilibrium requires that where the upper end of the conductor in Figure 31.9 is at a higher electric potential than the lower end. Thus, a potential difference is maintained between the ends of the conductor as long as the conductor continues to move through the uniform magnetic field. If the direction of the motion is reversed, the polarity of the potential difference is also reversed. when the moving conductor is part of a closed conducting path. The magnetic flux through that area is Because the resistance of the circuit is R, the magnitude of the induced current is power delivered by the applied force is = Iɛ =I2R Question :Consider the circuit .the length of the moving rod is 0.2 m, its speed is 0.1m/s , the magnetic field-strength is 1T ,)and the resistance of the circuit is 0.02Ω) 1.What is the emf generated around the circuit? 2.What current flows around the circuit? 3.What is the magnitude and direction of the force acting on the moving rod due to the fact that a current is flowing along it? F 4.What is the power delivered by the applied force? F = Iɛ =I2R