Sir, can you explain in detail, what is the working principle of an alternating current
generator or alternator? Let us think about a single rectangular turn, placed in between north and south pole of
a magnet, as shown here. Say, this single turn loop, A A B C D, can rotate against axis small a a b
After 90 degrees clockwise rotation, the side, A B of the loop, comes in front of south pole
and side C D comes in front of north pole, as shown here
The magnetic flux, as we can see here, is form north pole to south pole
At this position, the tangential motion of the side, A B, is just perpendicular to the
magnetic flux lines. Therefore, rate of flux cutting by the conductor, A B is maximum here, and for that flux cutting
there will be an induced current in the conductor A B. As the rate of flux cutting is maximum
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
Now, if we apply Fleming's right hand rule here, we will see the direction of the induced current
And the direction of this induced current will be, from A A to B at the same time, the
conductor C D comes under north pole, and here also, if we apply Fleming right hand
rule, we will get the direction of induced current, and it will be from C to D
Now, after clockwise rotation of another 90 degrees, the turn A B C D comes at vertical
position again, as shown. At this position, the tangential motion of conductor A B and C D is just parallel to
the magnetic flux lines, hence there will be no flux cutting that is, no current in
the conductor. While the turn A B C D comes from horizontal position to vertical position, angle between
flux lines and direction of motion of conductor, reduces from 90 degrees to zero degrees and
consequently the induced current in the turn is reduced to zero from its maximum value
After another clockwise rotation of 90 degrees the turn again come to horizontal position
and here conductor A A B comes under n, pole and C D comes under s, pole, and here if we
again apply Fleming's right hand rule, we will see that induced current in conductor
A A B, is from point B to A A, and induced current in the conductor C D is from D to
C as at this position, the turn comes at horizontal position from its vertical position, the electric
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
D to C and from C to B. Just reverse of the previous horizontal position when the current was circulating as A A to
B, B to C, C to D and D to A A. While the turn further proceeds to its vertical position
the current is again reduced to zero. So if the turn continues to rotate, the current in the turn continually alternate its direction
So we have seen, how an alternating current is produced in a turn, which is rotated inside
a magnetic field. Now we cut the loop and connect its 2 ends with 2 slip rings and stationary terminals
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
will glow. This is our elementary model of alternator