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Introduction |
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We have seen in the previous lesson that a current carrying conductor when kept in a magnetic field experiences forces and torques. |
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Magnetic Flux |
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We have already seen how the concept of electric flux helped us to learn the electric field intensities around the charges. Similarly concept of magnetic flux too helps us to calculate magnetic field strengths around magnets or current carrying conductors. |
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The Experiment of Faraday and Henry |
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Faraday and Henry performed lots of experiments to learn about the connection between electricity and magnetism. The results of these experiments have led to the life styles of todays men, who made life easy by using lots of electrical applications. |
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Lenz's Law |
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The motion of the magnet in either direction causes a change in strength of the magnetic field linked with the coil and this causes a current to be induced in the coil. This induced current opposes the change in the magnetic field by producing its own magnetic field. |
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Motional e.m.f and Faraday's Law |
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Suppose a uniform magnetic field B perpendicular to the plane of paper point outward is represented in the region ABCD. A rectangular loop PQRS is pulled such that it moves with a velocity V. |
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Lenz's Law and Energy Conservation |
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If the north pole of the magnet is moved towards the coil, the upper face(U.F) of the magnet acquires the north polarity on closing the key between 2 and 3. |
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Fleming's Right Hand Rule |
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The direction of induced current can easily be predicted using Fleming's right hand rule. |
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Eddy Currents |
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Induced currents are produced not only in the wires, but also in the block of metals. If a metallic block is placed in a continuously changing magnetic field, induced currents are set up in the body of the metallic block. |
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Application of Eddy Currents |
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When a steady current passes through a moving coil galvanometer, the coil undergoes a torque and does not come to equilibrium position instantly. Hence the coil is wound over a metallic frame so that the eddy currents produced in the frame can damp the oscillation and brings the coil to the equilibrium position instantly. |
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Self Induction |
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When a current is established in a conductor, a magnetic field is produced in its vicinity. We can visualize this field in terms of magnetic flux. If steady current flows the number of lines of force at a given place would remain the same. |
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Mutual Inductance |
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We know that if a current builds up or varies in a coil, the flux change leads to induced e.m.f in the same coil. This can happen event mutually between two interacting coils are close together, and if current is passed in one of them, it sets up a magnetic flux surrounding itself. |
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Summary |
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Electromagnetic induction (E.M.I) is the phenomenon of generating EMF by changing the number of magnetic lines of force associated with a circuit. The EMF so generated is called induced EMF and the corresponding current is called induced current. |
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Numerical 01 |
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A loop of wire of area 1m2 is placed perpendicular to a uniform magnetic field of 1Wbm-2. If the field is uniformly increased to 2Wbm-2 in a time of 10 seconds, find the induced EMF. |
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Numerical 02 |
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A wire 40 cm long bent into a rectangular loop of 15 cm x 5 cm is placed perpendicular to the magnetic field whose flux density is 0.8Wbm2. Within 0.5 seconds, the loop is changed into a 10cm square and the flux density increases to 1.4 Wb m-2. Find the induced EMF. |
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Numerical 03 |
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A circular coil of radius 8.0 cm and 20 turns rotates about its vertical diameter with an angular speed of 50ms-1 in a uniform horizontal magnetic field of magnitude 3.0 x 10-2 T. |
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Numerical 04 |
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A copper disc of radius 10 cm rotates 1200 times per minute with its plane perpendicular to a uniform magnetic field. If the induced EMF between the edge and centre of disc is 6.284 mV, find the density of the field. |
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Numerical 05 |
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Find the EMF in a coil of 50 turns, each of area 80 cm2 when making 1800 revolutions per minute in a uniform field of flux density 6 x 10-3 T. |
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Numerical 06 |
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If the coefficient of mutual inductance of the primary and secondary coils of an induction coil is 6H and a current of 5A is cut off in 1/500 second, calculate the E.M.F f induced in the secondary coil. |
