Electromotive Force 

An electromotive force (EMF) is necessary to produce an electrical current. The production of electrical energy on a large scale cannot be accomplished economically with batteries. Most of the electricity produced today is created through the use of alternators and generators. Both machines operate on the principle of the induced voltage.

The conductor, which has its ends connected to a sensitive ammeter, is being moved rapidly downward in a magnetic field. As the conductor is moved down­ward, it cuts lines of magnetic flux. As a result, there is a deflection of the meter needle indicating the presence of an electrical current produced by an induced voltage. It is evident that the motion is responsible for the voltage generated since no current is present if the conductor doesn’t move or motionless. Further­more, the meter needle deflects in the opposite direction if the conductor is moved upward through the magnetic field. The direction in which an induced voltage is produced depends on the direction of conductor movement.

In general, the amount of induced voltage produced in a conductor is directly propor­tional to the

• Strength of the magnetic field.
• Length of the conductor in the field.
• Speed at which the conductor passes through the field.
• Angle at which the conductor passes through the field.

In machines that generate voltage, the strength of the field and the conductor length are fixed quantities. The cutting angle depends upon the rotation of the conductor. Therefore, the only real variable is conductor speed. As the conductor speed increases, more lines of force are cut per second, and the induced voltage increases in magnitude.

In generators and alternators, powerful electromagnets are used to establish a strong magnetic field. Conductors are mounted on an armature and rotated at high speeds through this field. A large number of conductors can be used so that the individ­ual voltages of all the conductors act in series to produce a greater voltage. In summary, a high voltage can be created by cutting a powerful magnetic field with a series of conductors moving at high speed.

Questionnaire:

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