DC Motors: How Do They Work? Construction & Working Principle of a DC Motor | Electrical4U

Summary

This video explains the working principle of a DC motor. It describes how a current-carrying conductor experiences mechanical force when placed in a magnetic field. Through a simple model, the flow of current in the conductors and the resulting torque that rotates the motor are explained using Fleming's Left-Hand Rule. The video highlights how the direction of current and the forces acting on the conductors produce rotational motion. Additionally, it explains how this principle is applied in a practical DC motor, where multi-turn armature coils and multiple poles are used.

Takeaways

• 😀 The working principle of a DC motor is based on the interaction between current-carrying conductors and magnetic fields.
• 😀 When a conductor carrying current is placed in a magnetic field, it experiences a mechanical force that pushes it in a specific direction.
• 😀 In the elementary model, a single conductor loop is placed between two poles of a magnet (north and south).
• 😀 DC current flows through the loop, with the positive terminal connected to the left conductor and the negative terminal to the right conductor.
• 😀 The conductors inside the magnetic field experience mechanical forces, which can be determined using Fleming's Left Hand Rule.
• 😀 Fleming’s Left Hand Rule: The forefinger represents the magnetic field, the middle finger represents the current, and the thumb indicates the direction of the force.
• 😀 The force on the left conductor is upward, while the force on the right conductor is downward, creating a torque that rotates the loop in a clockwise direction.
• 😀 After a 90-degree rotation, the conductors temporarily stop receiving current as the commutator segments disconnect them from the battery.
• 😀 Despite the temporary disconnection, the loop continues to rotate due to its moment of inertia until it reaches a horizontal position again.
• 😀 In a practical DC motor, the single turn is replaced with an armature coil, and there are more than two poles, making the motor more efficient and durable.

Q & A

What is the basic working principle of a DC motor?

The basic working principle of a DC motor is based on the interaction between a current-carrying conductor and a magnetic field. When a conductor carrying current is placed in a magnetic field, it experiences a mechanical force that causes it to move.

How does Fleming's Left-Hand Rule apply to the working of a DC motor?

Fleming's Left-Hand Rule is used to determine the direction of the force on a current-carrying conductor within a magnetic field. The rule states that if the forefinger points in the direction of the magnetic field (from North to South), and the second finger points in the direction of the current, the thumb will indicate the direction of the mechanical force.

What happens to the direction of current in the conductors when the commutator system is used in a DC motor?

The commutator system ensures that the direction of current in the conductors is always maintained in such a way that the motor continues to rotate in the same direction. As the armature rotates, the commutator reverses the direction of current in the conductors, ensuring continuous torque generation.

What is the role of the commutator in a DC motor?

The commutator in a DC motor reverses the direction of current in the armature conductors as the motor turns. This reversal ensures that the force acting on the conductors continues to rotate the armature in the same direction, allowing the motor to keep running.

Why does a DC motor continue to rotate after the current stops flowing in the conductors at 90 degrees?

Even when the current stops flowing at 90 degrees due to the commutator's position, the armature continues to rotate due to its momentum. The inertia of the rotating armature helps it complete its rotation until the current is reintroduced.

What is the effect of the magnetic field on the conductors in a DC motor?

The magnetic field exerts a mechanical force on the current-carrying conductors. This force is responsible for generating torque, which causes the rotation of the armature and, in turn, the rotation of the motor shaft.

How does the direction of mechanical force change in the conductors during each rotation cycle of the motor?

As the armature rotates, the direction of the mechanical force on the conductors also changes. When the conductors move under different poles of the magnet (North and South), the force directions alternate between upward and downward, which continues to drive the armature's rotation.

What is the difference between the simplified model of a DC motor and a practical DC motor?

In the simplified model of a DC motor, only a single turn of conductor is used, whereas in a practical motor, there are multiple turns of the armature coil. Additionally, practical DC motors can have more than two magnetic poles, improving their efficiency and performance.

What is the purpose of using multiple turns in the armature coil in a DC motor?

Using multiple turns in the armature coil increases the total amount of current-carrying conductor in the magnetic field, which results in a greater force and, consequently, more torque. This makes the motor more efficient and powerful.

What happens when the motor reaches the vertical position in its rotation?

When the motor reaches the vertical position (90 degrees from its starting point), there is no current flowing in the armature conductors because the commutator segments interrupt the circuit. However, the armature continues to rotate due to its momentum until the current is reestablished.