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| Electric Generator (DC Generator) |
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| The electric generator is a machine for producing electric current. The electric generator or dynamo converts mechanical energy into electrical energy. |
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| DC Generator |
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| The generator is an application of electromagnetic induction. It works on the principle that when a wire is moved in a magnetic field, then the current is induced in the coil. A rectangular coil is made to rotate rapidly in the magnetic field between the poles of a horse shoe type magnet. When the coil rotates, it cuts the lines of magnetic force, due to which a current is produced in the generator coil. This current can be used to run the various electrical appliances. |
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| A simple D.C. generator consists of a
rectangular coil ABCD which can be rotated rapidly between the poles N and S
of a strong horse-shoe type magnet M. The generator coil is made of a large number of turns of insulated copper wire. The two ends of the coil are connected to the two copper half rings (or split rings) R1 and R2 of a commutator. There are two carbon brushes B1 and B2 which press lightly against the two half rings. When the coil is rotated, the two half rings R1 and R2 touch the two carbon brushes B1 and B2 one by one. So the current produced in the rotating coil can be tapped out through the commutator half rings and into the carbon brushes. From the carbon brushes B1 and B2 we can supply current into various electrical appliances like radio,
television, electric bulb etc. |
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| Let us suppose that the generator coil ABCD is initially in the horizontal position. As the coil rotates in the anticlockwise direction between the pole N and S of the magnet the side AB of the coil moves down cutting the magnetic lines of force near the N-pole of the magnet and side DC moves up, cutting the lines of force near the S-pole of the magnet. Due to this, induced current is produced in the sides AB and DC of the coil. On applying Fleming's right hand rule to the sides AB and DC of the coil we find that the currents in them are in the directions B to A and D to C respectively. Thus the induced currents in the two sides of the coil are in the same direction and we get an effective induced current in the direction BADC. Due to this the brush B1 becomes
the positive pole and brush B2 becomes the negative pole of the generator. |
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| After half revolution, the sides AB and DC of the coil will interchange their positions. The side AB will come on the right hand side and starts moving up whereas side DC will come on the left hand side and start moving down. But when sides of the coil interchange their positions, then the two commutator half rings R1 and R2
automatically change their contacts from one carbon brush to the other. Due
to this change, the current keeps flowing in the same direction. Thus a DC
generator supplies a current only in one direction. |
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