Magnetic Effects Of Current

MAGNETIC EFFECT OF CURRENT


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ELECTRIC MOTOR


       An electric motor is a device that converts electric energy in mechanical energy. Electric motors are used in many electrical appliances such as tape recorders, refrigerators, toys, fans, mixers-grinders, juicers, washing machines, air conditioners, coolers etc. an electric motor is also called as Direct Current Motor or D.C. motor because it works on D.C. current.



Electric Motors     Electric Motors


Principle of Electric Motor

       An electric motor works on the principle that when a current carrying conductor capable to move freely is placed in a magnetic field, it experiences a mechanical force and begins to rotate in a direction given by Fleming’s left hand rule.

Construction of Electric Motor

       An electric motor consists of following important parts:

1. Armature

       Armature is a rectangular coil ABCD of insulated copper wire which is wrapped around a soft iron core and placed between the two poles of a U shaped permanent magnet.

2. Commutators

       Commutators are two half rings made up of copper which links the brushes to the coil. In the diagram, commutator rings are represented as C1 and C2. The function of commutator rings is to ensure that the direction of current in the coil reverses every half time so that one side of the coil is always pushed upwards and the other side of the coil is pushed downwards.

3. Carbon brushes

       Electric motor consists of two carbon brush B1 and B2 which are pressed lightly against the C1 and C2 rings of the commutator respectively. The brushes B1 and B2 are connected respectively to positive and negative terminals of the battery. Thus, the current is supplied to the coil through these brushes.

Working of Electric Motor

       Initially, the coil ABCD is considered to be in horizontal position so that the plane of coil becomes parallel to that of the magnetic field. Now, pass an electric current through the coil ABCD, entering at point A and leaving at point D. on passing the current, the two arms AB and CD of the coil which are perpendicular to the direction of the magnetic field, experience force according to Fleming’s left hand rule. As the direction of current passing through arms AB and CD of the coil is opposite to each other, so the forces acting on them will also be opposite to each other. These opposite forces push one arm of the coil (AB) in downward direction and the other arm (CD) in upward direction. As a result of this, the coil starts to rotate in anticlockwise direction.



Diagram To Show working of Electric Motors


       When the coil completes its half rotation, the commutator rings C1 and C2 change their contact from one carbon brush to the other. Due to this, the direction of current in the coil is reversed. The reversal of current reverses the direction of forces acting on the two sides of the coil. Thus, the side of the coil which was pushed upward previously is now pushed down and the side which was pushed downward is now pushed up.

       In this way, the whole process is repeated again and again to continuously rotate the coil.


Test Your Understanding and Answer These Questions:




  1. What is an electric motor? Where is it used?

  2. Explain the principle of an electric motor?

  3. Explain the construction of an electric motor?

  4. Explain the working of an electric motor with the help of a diagram.

  5. What is the function of commutator in an electric motor?

  6. What is the function of carbon brushes in an electric motor?



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