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Chapter 31
Faraday’s Law
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?
4.What is the power delivered by the applied force?
= Iɛ =I2R