Name: Faraday’s Law of Induction and Lenz’s Law
Uploaded: 2019-07-19
Duration: 10 min 7 s
Description: Here is an interesting video on electromagnetic induction explaining Faraday's laws of induction and Lenz's law. Get in to it to understand more!

Question

Explain the principle, construction and working of a DC motor.

Accepted Answer

Electric motor is a device by which electrical energy can be converted into mechanical energy.

DC motor is based on the principle of magnetic effect of electric current, which states that, when a current carrying conductor is placed in a magnetic field, it experiences a mechanical force.

Construction : A DC motor consists essentially of a coil ABCD (called armature) held between pole pieces (N, S) of magnet. The two ends of the armature are connected to the two split rings (S₁ and S₂). Two brushes B₁ and B₂ keep their contact with the split rings as the axle rotates.

Working : The DC current (from a battery) is passed via brushes and commutator through armature, when the plane of the coil ABCD is parallel to the magnetic field. According to Fleming's left-hand rule, the AB of the coil experiences a downward force; while the side CD experiences an upward force. Now these two equal, but opposite forces acting at AB and CD constitutes a couple, which rotates the coil. The couple is maximum when the plane of coil is parallel to magnetic field lines. But it goes on decreasing and becomes zero when the coil becomes perpendicular to magnetic lines of force. Consequently, the coil should stop at this position. However, due to inertia of the moving coil, it crosses this position and the coil again becomes parallel to the magnetic lines of force.

The contact of the brushes (B₁ and B₂) with the split-rings (S₁ and S₂) gets reversed and the current starts flowing along DCBA. Consequently, the side DC of the coil starts moving downwards, while the limb AB of the coil starts moving upwards in accordance with the Fleming's left-hand rule. In this way, the motion of the armature is always same.

The function of split-rings is to change the direction of current in the rectangular coil after every half revolution. This ensures the rotation of armature in the same direction throughout the working.

In simple electric motors, permanent magnets are used to produce magnetic field. In commercial electric motor, electromagnets are used to produce magnetic field.

Explain the principle, construction and working of a DC motor.

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