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Fleming’s Left-Hand Rule and Right-Hand Rule Explained in Detail

Electromagnetism
Electromagnetism

The Fleming’s left and right-hand thumb rules, in the late 19th century, were given by John Ambrose Fleming, an English electrical engineer. These rules are a simple way to determine the direction of motion of a given conductor in an electric motor at the moment when the direction of the current and magnetic field is known. 

This article will cover in detail the explanation of Fleming’s left & right-hand rules, their applications and uses.

Electromagnetism

Before learning the concepts of Fleming’s left and right-hand rules, it is important to know why and where it is applied. The electromagnetic force is a fundamental force in nature that takes place between two charged particles. It occurs when charged particles and uncharged magnetic force fields interact with the electric conductors and create electromagnetic fields.

This process introduces current in the conductor, which in turn creates magnetic lines of force in it. The magnetic field generated in the wire is the positive charge, that is, the current moving in a wire. To determine the direction of magnetic lines of force flowing in a conductor, Fleming’s right rule is used.

The relation between the current, the magnetic field and force are determined by these rules. If a current-carrying conductor is placed in a magnetic field, a certain force is generated on the conductor, and the direction of this force is determined by Fleming’s left-hand rule.

Similarly, if the conductor is brought and placed in a magnetic field, the current will be induced in the conductor. The direction of this current can be determined by using Fleming’s right-hand rule.

A key point to remember here is that only the direction of these three parameters (current, magnetic field and force) can be determined, not the scale or magnitude of the force in the magnetic field. 

Fleming’s Left-Hand Rule

This rule is used to determine the direction of the force that is induced in a current-carrying conductor when it is placed in the magnetic field. The force that is induced in the conductor is perpendicular to the directions of the magnetic field and the current.

The below figure shows how to hold out the left hand; the thumb, forefinger and middle finger are perpendicular to each other. 

The middle finger represents the flow of current in the conductor, the forefinger represents the direction of the magnetic field, and the thumb represents the direction of the force. 

Fleming’s Right-Hand Rule

Fleming’s right-hand rule is used to determine the direction of current induced whenever a conductor is placed forcefully inside the magnetic field. The relation among the three parameters, the direction of the magnetic field, applied force and the current, is understood by Fleming’s right-hand rule.

The below figure shows how to hold out the right hand; the forefinger, middle finger and thumb are placed perpendicular to each other, with the palm facing sideways. 

The forefinger determines the direction of the magnetic field, the middle finger determines the direction of induced current, and the direction of the thumb determines applied force.

A key point to remember while applying Fleming’s right-hand rule is not to confuse it with Maxwell’s right-hand thumb rule. Maxwell’s right-hand thumb rule determines the direction of the magnetic field when the direction of current is known, whereas Fleming’s right-hand rule determines the direction of induced current.

Rules to Remember

  • Fleming’s left-hand rule can be related to FBI, where ‘F’ stands for Force, ‘B’ stands for magnetic flux density, and ‘I’ stands for direction of the current. Assign these letters ‘F’, ‘B’, ‘I’ to the thumb, forefinger and middle finger of the left hand. This is how remembering which finger represents what parameter will come easy, and it will be easy to determine the directions of current, force and magnetic field.
  • The same method is applicable for Fleming’s right-hand rule where the keywords ‘F’, ‘B’, ‘I’ are assigned to the thumb, forefinger and middle finger of the right hand. 
  • Fleming’s right-hand rule follows Faraday’s law of electromagnetic induction, where a conductor is placed inside the magnetic field, and the current is induced as the result of it. In contrast, Fleming’s left-hand rule only determines the direction of the force when a current-carrying conductor is introduced to the magnetic field.

Applications of Fleming’s left and right-hand rules

Real-life applications of Fleming’s left and right-hand rule are listed below:

  • Different types of electric motors like AC, DC, Brushless, brushed, Induction uses the concept of how force is generated when a current-carrying conductor is kept under the magnetic field. Fleming’s left-hand rule can describe the flow of motion within these motors.
  • A standard electric motor is built with a rotor and stator, where the rotor is within the stator and is free to rotate. When current is passed through the copper wires around the rotor, the electromagnetic field is created. 
  • It interacts with the magnetic field of magnets in the stator. The way an electric motor is built makes Fleming’s left-hand rule possible to determine the physical force induced in the motor.
  • An electric generator works on the principle of electromagnetic induction, which is explained at the beginning of this article. Fleming’s right-hand rule is used to determine the direction of current in an electric generator.
  • If a coil attached to the circuit is placed in a magnetic field, an electric current is induced in the coil due to the law of induction. 
  • Applying Fleming’s right-hand rule, three fingers are stretched in the direction perpendicular to each other, which determines the flow of current induced in the coils of the electric generator.

Summing up

These two rules are the simple rules to determine the direction of induced current in generators and the direction of a force in motors using Fleming’s right-hand rule and Fleming’s left-hand rule, respectively. Many times Fleming’s right-hand rule is confused with Maxwell’s right-hand thumb rule. 

But if concepts of both the rules are memorised, both the rules work wonders. You can quickly determine the direction of induced current with Fleming’s rule and the direction of the magnetic field with Maxwell’s rule when the direction of current is already known.

Read also:  Logarithm And Its Application

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