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Electric Motor

  • Last Updated : 28 May, 2021

An electric motor used to generate mechanical power in the form of rotation. Let’s look at an example: What is the purpose of the electric fan in your home? It starts rotating when the switch is turned on and starts blowing air by rotating its blades. So what would be the answer if someone asked about its working? Is it because of electricity? No, electricity is the method to start the electric fan that is the conversion of electrical energy into mechanical energy. But how is the conversion of electrical energy into mechanical energy take place? What happens inside the electric motor? Let’s discuss it.

What is an Electric Motor?

An electric motor is a machine that is used to convert electrical energy into mechanical energy. When a current-carrying conductor is placed in the magnetic field it experiences some forces that help in the rotation of the shaft or axil.

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A motor is a piece of machinery that transforms electrical energy into mechanical energy. A mixer, for example, has spinning blades that mash and combine ingredients. The electric energy input to the mixer is converted into mechanical energy of the blade rotating, resulting in the desired action.



Principle of an Electric Motor

  • A motor operates on the principle of the current magnetic effect. When a current-carrying conductor generates a magnetic field around it then a force acts on a current-carrying conductor when it is placed perpendicular to the magnetic field.
  • When a rectangular coil is put in a magnetic field and current is transmitted through it, a force acts on the coil, causing it to spin continuously.
  • Consider the poles of two bar magnets held facing each other, separated by a narrow scape. A small length of conducting wire is formed into a loop and placed in the gap between the magnets so that it is in the magnetic field created by the magnets. As the loop’s ends are wired to the battery terminals, the loop begins to spin. This is due to the magnet’s magnetic field interfering with the electric current passing into the conductor. The induced South Pole is drawn to the North Pole due to the magnetic poles induced in the circle, and vice versa. As the current in the circle reverses, the caused the South Pole becomes the North Pole and is drawn to the magnet’s south pole. This leads the circle to spin indefinitely.

Fleming’s Left-Hand Rule

The first finger, middle finger, and thumb of your left hand should be stretched perpendicular to each other in such a way that the first finger represents the direction of the magnetic field, the middle finger represents the direction of the current in the conductor, and the thumb indicates the direction of motion of the conductor, according to Fleming’s left-hand rule.

Construction of an Electric Motor

Construction of an Electric Motor

Following are the main parts of the motor as shown in the figure above, with their respective functions: 

  1. Battery: A Battery is the DC power source that is frequently connected to a basic motor. It supplies DC current to the armature coil.
  2. Brushes: There are two carbon brushes present in the electric motor which serve as a connection between the commutator and the battery terminals.
  3. Permanent magnet: generates a strong magnetic field.
  4. Split ring type commutator: The reversal of current in the armature coil is takes place with the help of the commutator. It is made up of two metallic ring halves. The armature coil’s two ends are connected to these two halves’ metallic ring.
  5. Armature core: The armature coil is held in place by the armature core and also provides mechanical support to the coil.
  6. Armature coil: It is made up of single or multiple rectangle-shaped loops of insulated copper wire.
  7. Axle or Shaft: It is the place where the exchange of mechanical power takes place. The armature core and the commutator are mounted on the shaft.

Working of an Electric Motor

Working of an Electric Motor

  1. Initially, Brush B1 makes contact with the commutator half-ring R1, whereas brush B2 makes contact with the commutator half-ring R2. Current flows from A to B along coil side l1 of the rectangular coil ABCD, and from C to D along coil side l2. The magnetic field is directed from the magnet’s North pole to its South pole.
  2. The force F on the coil side l1 of the coil is in a downward direction, but the force F on the coil side l2 of the coil is in an upward direction, according to Fleming’s Left-hand rule. As a result, the coil’s side l1 is pulled down while its side l2 is pushed up. This causes the coil ABCD to revolve counterclockwise.
  3. When the coil reaches a vertical position while rotating, the brushes will contact the gap between the two commutator rings which cut off the flow of the current i in the coil. Despite the fact that the current i to the coil is cut off when it reaches the exact vertical position, the coil continues to rotate because it has momentum and has moved beyond the vertical position.
  4. When the coil moves beyond the vertical position after the half revolution, the coil’s side l2 moves to the left, while the coil’s side l1 moves to the right, and the two commutator half rings automatically change contact position from one brush to the other that is Brush B1 makes contact with the commutator half-ring R2, whereas brush B2 makes contact with the commutator half-ring R1. This makes the coil’s current i flow in the other direction.
  5. Now, the force acting on the sides l1 and l2 of the coil is reversed when the current i direction is reversed. The coil’s side l2 is now on the left, with a downward force F applied to it, while the side l1 is now on the right, with an upward force F applied to it. As a result, the coil’s side l2 is pulled down and the coil’s side l1 is pushed up. This causes the coil to rotate counterclockwise.
  6. After every half rotation, the current in the coil is reversed, and the coil continues to revolve as long as electricity from the battery is transmitted through it.

Uses of an Electric Motor

Electric motors are utilized for a wide range of purposes. The following is a list of some of them.

  1. Electric cars: Electric cars used in traveling. and it is pollution-free.
  2. Rolling mills: Rolling mills used to decrease the width of the hard material like metals.
  3. Electric cranes: Electric cranes used to lift heavy objects.
  4. Lifts: Basically used in big buildings.
  5. Drilling machine: A drilling machine used to make a hole in the walls or woods
  6. Fan: Fans are used for blowing air.
  7. Hairdryers: Hairdryers used to dry wet hair.
  8. Tape recorder: A tape recorder used to record the audio or video.
  9. Washing machine: The washing machine is the wash the clothes.
  10. Mixers: Mixers are used to mash and mix things.

The efficiency of a motor to be roughly about 70 – 85% as the remaining energy is wasted in heat production and sounds emitted.

Sample Problems

Problem 1: State Fleming’s left-hand rule.

Solution:

Fleming’s left-hand rule state that the first finger, middle finger, and thumb of your left hand should be stretched perpendicular to each other in such a way that the first finger represents the direction of the magnetic field, the middle finger represents the direction of the current in the conductor, and the thumb indicates the direction of motion of the conductor, according to Fleming’s left-hand rule.



Problem 2: What is the principle of an electric motor?

Solution:

A motor operates on the principle of the current magnetic effect. When a current-carrying conductor generates a magnetic field around it then a force acts on a current-carrying conductor when it is placed perpendicular to the magnetic field.

Problem 3: What is the role of the split ring in an electric motor?

Solution:

The reversal of current in the armature coil takes place with the help of the commutator. It is made up of two metallic ring halves. The armature coil’s two ends are connected to these two halves metallic ring.

Problem 4: How will you find out the direction of the magnetic field produced by the current-carrying conductor?

Solution:

Maxwell’s right-hand thumb rule is used to determine the direction of the magnetic field lines created by a straight wire carrying electricity. Imagine that the current-carrying wire is in the right hand, with the thumb pointing in the direction of the current, and the direction in which the fingers encircle the wire determines the direction of magnetic lines of force around the wire.

Problem 5: What is the difference between a bar magnet and an electromagnet.

Solution:

Following are the difference between a bar magnet and an electromagnet:

 Bar MagnetElectromagnet
1.It is a permanent magnet.It is a temporary magnet.
2.It generates a relatively weak attracting force.It generates a powerful magnetic field.
3.A bar magnet’s strength cannot be altered.An electromagnet’s strength can be altered by altering the number of turns in its coil or the current flowing through it.
4.A bar magnet’s polarity is set and cannot be changed.Changing the direction of current in an electromagnet’s coil can change its polarity.



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