In this article, we
shall discuss the **working principle of a DC Motor (Direct Current Motor)**.
So let us start with the basic introduction of the DC Motor.

# Introduction to DC Motor

A DC machine that
converts direct current electrical energy into rotational mechanical energy is
known as a **DC motor**. Hence, the DC motor is an electromechanical energy
conversion device. It has two major parts namely, the field system and armature.
The field system generates the required working magnetic flux in the machine
and the armature is the part that is free to rotate and it is a system of
conductors.

DC motors are used to
drive many types of mechanical loads in industries such as drive fans,
pumps, cranes and hoists, etc.

# Working Principle of DC Motor

The dc motor works on
the principle of electromagnetic interaction. According to this principle,
whenever a current-carrying conductor is placed in a magnetic field, the
conductor feels an electromagnetic force acting on it.

The magnitude of this
electromagnetic force is,

- Directly proportional
to the magnetic flux density (
*B*). - Directly proportional
to the current through the conductor (
*I*). - Directly proportional
to the length of the conductor (
*l*).

Therefore, the
magnitude of the electromagnetic force is given by,

**Explanation:**

To understand the
working principle of the dc motor, consider the simple single-coil motor as
shown in the following figure.

When an electric
supply is given to the coil, an electric current *I* starts flowing
through the coil. As we can see that the coil sides are placed under the
influence of a magnetic field of flux density *B* weber per sq. meter.
Consequently, each coil side experiences a force that is given by,

Since the two
coil sides are under the influence of opposite magnetic poles of the same pole strength,
therefore, the force acting on them will be equal and opposite.

Now, if d is the distance
between two coil sides, then the developed torque in the coil is given by,

`\Ï„=F.d`

`\⇒Ï„=BIld`

`\∴Ï„=BIA" "…(2)`

Where, *A = l.d*,
area of the coil.

This torque
developed in the coil rotates the coil and therefore, we obtain mechanical
energy in the form of rotation of the coil.

This is how a dc
motor works and converts dc electrical energy input into mechanical energy
output.

# Direction of Rotation of DC Motor

Now, let us know
how to determine the direction of rotation of the dc motor.

The direction of
force acting on a current-carrying conductor placed in a magnetic field is
identified by **Fleming’s Left-Hand Rule (FLHR)**.

According to Fleming’s left-hand rule, if the thumb, forefinger, and middle finger of the
left hand are kept mutually perpendicular to each other, and if the forefinger
points to the direction of the magnetic flux, the middle finger points to the
direction of electric current through the conductor, then the thumb will point
to the direction of electromagnetic force acting on the conductor.

The graphical
representation of Fleming’s left-hand rule is shown in the figure below.

Hence, this is all about the operating principle of the dc motor. In conclusion, a dc motor converts dc electrical energy into mechanical energy according to the law of electromagnetic interaction, i.e. interaction between a current-carrying conductor and a magnetic field.