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CHAPTER-30

CHAPTER-30. Induction and Inductance. Ch 30-2 Two Experiments. First Experiment: An ammeter register a current in the wire loop when magnet is moving with respect to loop. Faster motion causes more current By changing the polarity of magnet facing the coil plane, changes the current direction

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CHAPTER-30

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  1. CHAPTER-30 Induction and Inductance

  2. Ch 30-2 Two Experiments • First Experiment: An ammeter register a current in the wire loop when magnet is moving with respect to loop. • Faster motion causes more current • By changing the polarity of magnet facing the coil plane, changes the current direction • Second Experiment: An ammeter register a current in the left-hand wire loop just as switch s is opened or closed. No motion of coil is involved • Emf induced in the loop when something is changing in the loop

  3. Ch 30-3 Faraday’s Law of Induction • Faraday’s Law: •  = -N dB /dt= - d(B.A)/dt • N is number of coils • Three cases: • B changing with time •  = -N A cos (dB /dt) • Coil Area A changing with time •  = -N B cos (dA /dt) • Angle between B-direction and coil-plane is changing with time •  = -N AB (d (cos) /dt) • Faraday’s Law :An emf is induced in the loop in the previous experiments when the number of magnetic field lines that passes through the loop is changing. • Magnetic Flux through a loop: B= B.dA= B dA cos B =BA(BA, B uniform) • Unit of B : Weber (Wb) 1 Wb= 1T.m2 • Faraday’s Law:  = - dB /dt = - d(B.A)/dt The magnitude of the emf  induced in a conducting loop is equal to rate at which the magnetic flux is changing through that loop with time

  4. Ch 30-4 Lenz’s Law- definition of direction of induced current in the loop Lenz’s Law: An induced emf has a direction such that the magnetic field due to the current opposes the change in the magnetic flux that induces the current • Opposition to Pole movement: • Opposition to Flux change:

  5. Ch 30-4 Lenz’s Law- definition of direction of induced current in the loop • Opposition to Flux change

  6. Ch 30-5 Induction and Energy Transfer • A closed conducting loop is pulled out of a magnetic field at constant velocity v. While loop is moving a current I is induced in the loop and the loop segments still within magnetic field experiences forces F1, F2 and F3. • As the loop moves towards right, flux through the coil decreases, induced current will be clockwise •  = B d(A)/dt= B d(Lx)/dt =BLdx/dt=BLv i=  /R=BLv/R; Power Disipated Pdis=i2R=B2L2v2/R • Rate of doing work P=|F3|v F3=iLB=B2L2v/R; P=|F3|v= (B2L2v/R) x v =B2L2v2/R

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