Electric Motor: Meaning, Classification, and Principle

Electric Motor is one of the greatest inventions by mankind. The life we are leading today is due to the invention of the motors, or else we would have been just glowing bulbs with electricity. The electric motor transforms electrical energy into mechanical energy.

An Electric motor is generally developed for continuous rotation. Precisely speaking, the electric motor is used for producing rotational energy. Electric Motor is a device that we all use every day in our activities. In this article, we will provide detailed information on Electric Motor. Scroll down to find out more!

Practice Embibe’s Exclusive CBSE Term 1 Sample Papers Based on New Guidelines:

What is an Electric Motor?

In simple words, an electric motor is a device that converts electrical energy to mechanical energy. When we talk about mechanical energy here, it means rotational or circular movement. Due to the electromagnetic action, the parts of the motor turn or rotate. This rotational movement has applications in all the devices mentioned above.

Different Types of Electric Motors

Based on the source of electricity, motors are divided into:
1. DC motor
2. AC motor
All motors have mainly two parts – Rotor and Stator
Rotor: It is the rotating part of the motor. Based on the type of motor, either the magnetic part or the coils can be in the rotor.
Stator: It is the stationary part of the motor. As above, depending on the type of motor, either the magnetic part or the coils can be in the stator.
We can classify the motors as below:

What is the Principle of an Electric Motor?

We owe the electric motor to the work of many scientists. Electric current passing through a conductor creates a magnetic field around it. Hans Christian Oersted first observed this in the \({19^ {{\text{th}}}}\) century. This phenomenon is called the magnetic effect of electric current. Andre Marie Ampere, a French scientist, demonstrated that a current-carrying conductor placed in a magnetic field experiences a force that makes the conductor move. Michael Faraday, an English scientist, showed that a moving field creates an electric current. The experiments of them and many other scientists helped develop machines such as motors and generators.

A current-carrying conductor is placed in a magnetic field. It experiences a force that makes it move in a direction perpendicular to both the field and the current. We can find the direction of movement by Fleming’s left-hand rule as given in the above diagram.
Let us see the working of a few types of motors.

Working of DC Motor

It runs using direct current \({\text{DC}}\) To understand its working, let us simplify its construction to a single-coil between two poles.

Current flows from \(A\) to \(B\) near the north pole and from \(C\) to \(D\) in the side near the south pole. Thus, the current direction and the field lines are perpendicular to each other. So, the sides \(AB\) and \(CD\) experience a force whose direction is given using Fleming’s left-hand rule.
Side \(AB\) experiences an upward force, and side \(CD\) experiences a downward force. So, the rectangular coil \(ABCD\) moves circularly. After the half rotation, due to the split ring, current flows in the direction \(D\) to \(C\) near the north pole and \(B\) to \(A\) near the south pole. So, there is no change in the direction of the force on both sides, and the coil rotates continuously.
A practical \({\text{DC}}\) motor has many coils wound over a core, called an armature. Their ends are connected to the split rings, called commutators. Brushless motors do not use commutators.
Small motors use permanent magnets. Bigger motors use electromagnets. Based on the way the windings are done for the electromagnet poles and the armature are connected, \({\text{DC}}\) motors are classified as:
a. Separately excited \({\text{DC}}\) motor: There are two separate windings for the poles and the armature.

b. Self-excited \({\text{DC}}\) motor: Both the poles and the armature are connected to the same supply. Types of self-excited motors are:
i. Series \({\text{DC}}\) motor: The coils for the poles and the armature are in series, that is, the same current flows through both of them.

ii. Shunt \({\text{DC}}\) motor: The coils for the poles and the armature are in parallel to each other.

iii. Compound \({\text{DC}}\) motor: It is a combination of both series and shunt motors.

AC Motors

AC motors run on alternating current (AC) supply. By using alternating current, the magnetic field can be made to rotate. The speed of rotation of the field is called synchronous speed. The synchronous speed can be calculated from the equation,
\( {N_s} = \frac{ {120f}}{P}\)
where,
\(N_s\) is the synchronous speed, in rpm (revolutions per minute)
\(f\) is the frequency of the AC supply, in hertz \(\left({Hz} \right)\)
\(P\) is the number of magnetic poles
They can be classified as:
a. Synchronous motor
b. Induction motor

Synchronous Motor

In a synchronous motor, the armature is magnetically locked with the field. Therefore, it rotates along with it at the same speed as the field. Therefore, it is called a synchronous motor.
Based on the phase of the AC supply, synchronous motors can be-
i. Single-phase synchronous motor
ii. Three-phase synchronous motor

Induction Motor

The magnetic field rotates at synchronous speed, but the armature does not rotate at the same speed but is slightly slower. There is a slip between the magnetic field speed and the speed of the rotor. Therefore, induction motors are also called asynchronous motors.
Based on the AC supply, induction motors can be-
i. Single-phase induction motor:
Just as in single-phase synchronous motors, a rotating magnetic field is created in the stator winding by using capacitors or split windings. Low power devices like home appliances use single-phase induction motors.
ii. Three-phase induction motor:
They are also called self-starting motors as they do not require any extra winding, capacitors, or special devices to start them. So these motors are the simplest of all types of motors.
As the name says, it works on the principle of mutual induction. There are two types of rotors, squirrel cage and phase wound type (also called slip ring rotor). Both these types are closed circuits. A varying magnetic field in the stator creates mutual induction in the rotor. As a result, a current is induced in the rotor windings. The magnetic field created by this induced current acts on the field of the stator winding. This interaction between stator field and rotor field is the principle of rotation of the rotor in the same direction of the stator field.

Applications of Electric Motors

As written at the beginning of this article, we see motors at homes and in industries. Some of the applications of motors based on their types are:

Permanent Magnet Motors

They are usually small applications. For example, they are used in toys, computer drives, car wipers, portable blowers, vibrators in cellphones.

Series Motors

They are used where heavy loads are present. Some of the uses are in cranes, lifts, hoists, conveyors, sewing machines.

Shunt Motors

They are used when accurate speed control is required. Some of the applications are in drilling machines, lathes, blowers, fans, centrifugal pumps.

Compound Motors

They combine the properties of series and shunt motors. Elevators, rolling mills, conveyors are some of the applications.

NCERT Solutions for 12th Physics Chapter 12

Synchronous Motors

They are used when accurate speed is needed. Precise speed is needed in systems such as servo motors, aircraft gyrocompasses and robotics. Disc players, electric clocks, timers, turntables are some of the applications of synchronous motors.

Induction Motors

Home appliances like refrigerators, vacuum cleaners, air-conditioners, fans, mixers, water pumps, hairdryers are some of the applications of single-phase induction motors.
Industrial and heavy-duty applications such as compressors, grinders, flour mills, hoists, lifts, cranes use three-phase induction motors.

Solved Examples on Electric Motor

Summary

In this article, we have seen how the inter-relation between electricity and the magnetic field is put to use to create a moving force. Based on the source of electricity, motors are divided into two types namely, DC and AC motors. We use different types of motors depending on the source of electricity, its types, and also the nature of work to be done. Some work involves heavy loads, while some require the right speed. The construction of motors and their windings too change based on the source and the work to be done by them.

FAQs on Electric Motor

Q.1. What does an electric motor convert electrical energy into?
Ans: An electric motor converts electrical energy into mechanical energy. It creates a rotational movement.

Q.2. What are the types of motors based on electric supply?
Ans: Based on the electric supply, motors can be direct current \(\left({DC} \right).\) or alternating current AC motors.

Q.3. What are the two main parts of any motor?
Ans: A motor rotates when it receives an electrical supply. So any motor has two main parts called stator and rotor. The stator is the stationary or fixed part of the motor. The rotor is the rotating part of the motor.

Q.4. When using Fleming’s left-hand rule, what direction is signified by the thumb?
Ans: The thumb signifies the direction of the force that causes the movement of the conductor in a magnetic field.

Q.5. Why is a synchronous motor called so?
Ans: The magnetic field rotation speed when AC is supplied to the armature is called synchronous speed. The rotor also runs at the same speed in a synchronous motor.

We hope this detailed article on Electric Motor helps you in your preparation. If you get stuck do let us know in the comments section below and we will get back to you at the earliest.