a single loop of conductor of rectangular shape is placed between two opposite poles

of magnet.

Let’s us consider, the rectangular loop of conductor is ABCD which rotates inside the magnetic field

about its own axis ‘ab’. When the loop rotates from its vertical position to its horizontal position, it cuts

the flux lines of the field. As during this movement two sides, i.e. AB and CD of the loop cut the flux

lines there will be an emf induced in these both of the sides (AB and BC) of the loop.

As the loop is closed there will be a current circulating through the loop. The direction of the current can

be determined by Flemming’s right hand Rule. This rule says that if you stretch thumb, index finger and

middle finger of your right hand perpendicular to each other, then thumbs indicates the direction of

motion of the conductor, index finger indicates the direction of magnetic field i.e. N – pole to S – pole, and

middle finger indicates the direction of flow of current through the conductor.

Now if we apply this right hand rule, we will see at this horizontal position of the loop, current will flow

from point A to B and on the other side of the loop current will flow from point C to D.

Now if we allow the loop to move further, it will come again to its vertical position, but now upper side of

the loop will be CD and lower side will be AB (just opposite of the previous vertical position). At this

position the tangential motion of the sides of the loop is parallel to the flux lines of the field. Hence there

will be no question of flux cutting and consequently there will be no current in the loop. If the loop rotates

further, it comes to again in horizontal position. But now, said AB side of the loop comes in front of N

pole and CD comes in front of S pole, i.e. just opposite to the previous horizontal position as shown in the

figure beside.

Here the tangential motion of the side of the loop is perpendicular to the flux lines, hence rate of flux

cutting is maximum here and according to Fleming’s right hand Rule, at this position current flows fromB

to A and on other side from D to C. Now if the loop is continued to rotate about its axis, every time the

side AB comes in front of S pole, the current flows from A to B and when it comes in front of N pole, the

current flows from B to A. Similarly, every time the side CD comes in front of S pole the current flows

from C to D and when it comes in front of N pole the current flows from D to C.

If we observe this phenomena in different way, it can be concluded, that each side of the loop comes in

front of N pole, the current will flow through that side in same direction i.e. downward to the reference

plane and similarly each side of the loop comes in front of S pole, current through it flows in same

direction i.e. upwards from reference plane. From this, we will come to the topic of principle of DC

generator. Now the loop is opened and connected it with a split ring as shown in the figure below. Split

ring are made out of a conducting cylinder which cuts into two halves or segments insulated from each

other. The external load terminals are connected with two carbon brushes which are rest on these split slip

ring segments.

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