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Working Principle of DC Motor
Working principle of D.C. motor is very simple. We can see that when the current conductor is placed in magnetic field, it experiences some force in particularly direction (picture 1.1).
picture 1.1: Conductor placed in magnetic field
The very basic construction of a D.C. motor contains a current carrying armature which is connected to the supply and through commutator segments and brushes. the armature is placed between north and south pole of a permit or an electromagnet in elementary model. One single turn of conductor is placed between two opposite poles if we start to supply D.C. via commutators system current will start to flow (picture 1.2).
picture 1.2: Basic construction of a DC motor
As we see positive terminal of a battery is connected to left conductor of a turn and a negative terminal is connected to right conductor of a turn. As we see in model north pole of the magnet is placed near left side and south pole is placed near right side of the turn (picture 1.3).
picture 1.3: Connection of battery and conductor with magnetic poles near
Current in left side flows inward and current in the right side flows outward as we see conductor is carrying current and they placed in magnetic field both of them experienced a mechanical force acted on them. Direction of mechanical force can be easily determined by applying Fleming’s left hand rule (picture 1.3) .
Fleming’s left-hand rule
To do this spread out your left thumb and forefinger and second finger so they are all at ninety degrees to one another (picture 1.4).
picture 1.4: Fleming’s left hand rule
With that if the forefinger is align along direction of magnetic field from the North Pole to the South Pole and second finger is align along direction of the current in left side conductor then thumb indicates direction of mechanical force.
picture 1.5: Direction of Thumb finger or mechanical force
Similarly if the fore finger is align along the direction of magnetic field from the North Pole to the South Pole and second finger is align along direction of the current in a right side conductor then thumb indicates direction of mechanical force due to this upward and downward forces on the turn (picture 1.6).
picture 1.6: Direction of Thumb finger or mechanical force
One torque is produced when turn rotates on clockwise direction as shown (picture 1.7) .
picture 1.7: One torque is produced when turn rotates on clockwise direction
After rotation of the Turn, turn comes to vertical position in respect of the magnetic field (picture 1.8).
picture 1.8: Turn comes to vertical position in respect of the magnetic field.
At this position there is no current in conductor because the turn conductor and brushes rest between two commutators. Hence there is no force acting on conductor by due to moment of inertia, turn continue to rotate and comes horizontal again, position of conductor has been changed, here that means conductor which was previously in left position comes to right position and which was previously in the right position comes to left position. At that position we can determine mechanical force with applying Fleming’s left hand rule let’s do that to do this spread out your left thumb, forefinger and second finger so they are all at ninety degrees to one to another. So if forefinger is align in direction of magnetic field. That is from the North Pole to South Pole and second finger is aligned in direction of a current in the left side conductor then thumb indicates direction of mechanical force this is clearly upward here (picture 1.9).
picture 1.9:How to determine mechanical force with applying Fleming’s left hand rule when conductor and brushes rest between two commutators
So if forefinger is align in direction of magnetic field that is from the North Pole to South Pole and second finger is aligned in the direction of a current in the right side conductor then from indicates direction of mechanical force this is clearly downward here. Do this upward and downward forces turn tends to rotate in clockwise direction from that explanation we can come to a conclusion that here in this model we can see that whichever conductor comes near South Pole experience upward mechanical force and near North Pole downward mechanical force. And do this continuously forces mechanical turn rotate even if battery is not connected particularly D.C. motor rotates at the same principle like this elementary model instead of single turn in D.C. motor we have mount turns on major coil and instead of two poles there is number of Poles installed.
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