WEBVTT

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Sir, can you explain in detail, what is the
working principle of an alternating current

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generator or alternator? Let us think about a single
rectangular turn, placed in between north and south pole of

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a magnet, as shown here. Say, this single turn
loop, A A B C D, can rotate against axis small a a b

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After 90 degrees clockwise rotation, the side,
A B of the loop, comes in front of south pole

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and side C D comes in front
of north pole, as shown here

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The magnetic flux, as we can see
here, is form north pole to south pole

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At this position, the tangential motion of
the side, A B, is just perpendicular to the

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magnetic flux lines. Therefore, rate of flux cutting by the
conductor, A B is maximum here, and for that flux cutting

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there will be an induced current in the conductor
A B. As the rate of flux cutting is maximum

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at this position, the induced current would also be maximum. As we know
that induced current is directly proportional to the rate of flux cutting

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Now, if we apply Fleming's right hand rule here,
we will see the direction of the induced current

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And the direction of this induced current
will be, from A A to B at the same time, the

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conductor C D comes under north pole, and
here also, if we apply Fleming right hand

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rule, we will get the direction of induced
current, and it will be from C to D

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Now, after clockwise rotation of another 90
degrees, the turn A B C D comes at vertical

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position again, as shown. At this position, the tangential
motion of conductor A B and C D is just parallel to

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the magnetic flux lines, hence there will
be no flux cutting that is, no current in

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the conductor. While the turn A B C D comes from
horizontal position to vertical position, angle between

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flux lines and direction of motion of conductor,
reduces from 90 degrees to zero degrees and

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consequently the induced current in the turn
is reduced to zero from its maximum value

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After another clockwise rotation of 90 degrees
the turn again come to horizontal position

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and here conductor A A B comes under n, pole
and C D comes under s, pole, and here if we

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again apply Fleming's right hand rule, we
will see that induced current in conductor

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A A B, is from point B to A A, and induced
current in the conductor C D is from D to

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C as at this position, the turn comes at horizontal
position from its vertical position, the electric

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current in the conductors, comes to its maximum value. That means,
current is circulating in the closed turn from point, B to A A, A A to D

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D to C and from C to B. Just reverse of the previous
horizontal position when the current was circulating as A A to

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B, B to C, C to D and D to A A. While the turn
further proceeds to its vertical position

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the current is again reduced to zero. So if the turn continues to
rotate, the current in the turn continually alternate its direction

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So we have seen, how an alternating current is
produced in a turn, which is rotated inside

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a magnetic field. Now we cut the loop and connect
its 2 ends with 2 slip rings and stationary terminals

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of a simple lamp circuit are placed on slip rings. When the loop rotates,
we will get an alternating current in the circuit due to which the lamp

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will glow. This is our elementary model of alternator