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Fleming's Left-Hand Rule and Fleming's Right-Hand Rule . 

Fleming’s Left-Hand Rule and Fleming’s Right-Hand Rule

What are Fleming’s Left-Hand Rule and Fleming’s Right-Hand Rule? . All electrical machines work on the principle of electromagnetic induction. According to this principle, if there is relative motion between a conductor and a magnetic field, then an EMF is induced in the conductor. On the other hand, if a current carrying conductor is placed in a magnetic field, the conductor experiences a force. For practical and analytical purposes, it is important to determine the direction of induced EMF and force acting on the conductor. Fleming’s hand rules are used for that.

Fleming's Left-Hand Rule and Fleming's Right-Hand Rule
Fleming’s Left-Hand Rule and Fleming’s Right-Hand Rule

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An English electrical engineer and physicist John Ambrose Fleming stated two rules in late 19th century to determine the direction of induced EMF and force acting on a current carrying conductor placed in a magnetic field. These rules popularly known as Fleming’s Left Hand Rule and Fleming’s Right Hand Rule.

Basically, both left hand rule and right hand rule show a relationship between magnetic field, force and current.

Fleming’s left hand rule is used to determine the direction of force acting on a current carrying conductor when it placed in a magnetic field, hence it is mainly applicable in electric motors. Whereas, Fleming’s right hand rule is used to determine the direction of induced EMF in a conductor moving relative to a magnetic field, thus it is mainly applicable in electric generators.

What Is Fleming’s Right-Hand Rule?

According to Faraday’s law of electromagnetic induction, when a conductor moves through a magnetic field, an electric current is induced in it. Fleming’s right-hand rule is used to determine the direction of the induced current.

Fleming’s-right-Hand-Rule
Fleming’s-right-Hand-Rule

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Fleming’s Right Hand Rule states that if we arrange our thumb, forefinger and middle finger of the right-hand perpendicular to each other, then the thumb points towards the direction of the motion of the conductor relative to the magnetic field, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the induced current.

Flemings-Right-Hand-Rule-for-Generators
Flemings-Right-Hand-Rule-for-Generators

Tips : Fleming’s right hand rule is applicable to electrical generators and alternators. That’s why it is also known as generator rule.

What is Fleming’s Left-Hand Rule?

When a current-carrying conductor is placed in an external magnetic field, the conductor experiences a force perpendicular to both the field and the current flow’s direction. Fleming’s left-hand rule is used to find the direction of the force acting on the current carrying conductor placed in a magnetic field.

Fleming’s-Left-Hand-Rule
Fleming’s-Left-Hand-Rule

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Fleming’s Left Hand Rule states that if we arrange our thumb, forefinger and middle finger of the left-hand perpendicular to each other, then the thumb points towards the direction of the force experienced by the conductor, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the electric current.

Flemings-Left-Hand-Rule-for-Motors
Flemings-Left-Hand-Rule-for-Motors

Tips : Fleming’s left hand rule is applicable to electrical motors, That’s why it is also known as Motor Rule.

Difference Between Fleming’s Left-Hand and Right-Hand Rule

Fleming’s Left-Hand Rule Fleming’s Right-Hand Rule
It is used for electric motors It is used for electric generators
The purpose of this rule is used for finding the direction of the magnetic force acting in an electric motor. The purpose of this rule is used for finding the direction of the induced current in an electric generator.
The middle finger represents the direction of the current The middle finger represents the direction of the induced current

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We can observe that the left-hand rule is applicable to Motors and the right-hand rule to Generators. Fleming’s left-hand rule and Fleming’s right-hand rule are a pair of visual mnemonics (mnemonics are learning techniques or memory aids, such as an abbreviation, rhyme or mental image that helps to remember something). In practice, these rules are never used except as a convenient trick to determine the direction of the resultant – either current or thrust. What gives the magnitude of force along this direction determined by these rules is the Lorentz’ Force.

Fleming’s Left-Hand Rule Examples

Q1. Determine the direction of the force acting on the proton if the proton moves towards the east by entering a uniform magnetic field in the downward direction.

Using Fleming’s left-hand rule, we can determine the direction of force acting on the proton.

Flemings-Left-Hand-Rule-And-Flemings-Right-Hand-Rule
Flemings-Left-Hand-Rule-And-Flemings-Right-Hand-Rule

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It is given that the proton is moving towards the east, and therefore, the motion of the current is towards the east. The direction of force is towards the north as the magnetic field is acting downwards. Consequently, we can say that the direction of the force acting is towards the north.

Q2. Find the direction of the magnetic field if an electron is moving vertically upwards and gets deflected towards the south due to a uniform magnetic field.

Using Fleming’s left-hand rule, we can determine the direction of the magnetic field acting on the electron.

Flemings-Left-Hand-Rule-And-Flemings-Right-Hand-Rule
Flemings-Left-Hand-Rule-And-Flemings-Right-Hand-Rule

We know that the charge on an electron is negative. When the electron moves upward, the direction of the current is in the opposite direction; that is, the direction of the current is downwards. It is given that the force acting on the electron is in the south direction. Therefore, the direction of the magnetic field is towards the east.

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Uses of Fleming’s Left-Hand Rule and Right-Hand Rule

Fleming’s Left-hand rule:

  • It is used to find the direction of the magnetic force acting on the current-carrying conductor placed in a uniform magnetic field.
  • Fleming’s Left-hand Rule can be used to evaluate the direction of the motion of the conductor placed in the magnetic field.
  • It can also be utilized for the determination of the direction of the electron or proton when the magnetic field is applied to it.
  • You can find its application in the working of electric motors.

Fleming’s Right-hand rule:

  • The main application of Fleming’s right-hand rule is to determine the direction of induced current in the conductor placed in the magnetic field.
  • You can find its application in the working of electric generator

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Frequently Asked Questions – FAQs

State Fleming’s right hand rule.

Fleming’s Right Hand Rule states that if we arrange our thumb, forefinger and middle finger of the right-hand perpendicular to each other, then the thumb points towards the direction of the magnetic force, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the current.

State Fleming’s left-hand rule.

Fleming’s Left Hand Rule states that if we arrange our thumb, forefinger and middle finger of the left hand perpendicular to each other, then the thumb points towards the direction of the magnetic force, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the current.

Which rule is used in electric motors?

Fleming’s Left-Hand rule is used in electric motors.

What is the purpose of Fleming’s right hand rule?

The purpose of Fleming’s right hand rule is to find the direction of induced current when a conductor moves in a magnetic field.

Which rule is used for electric generators?

Fleming’s right-hand rule is used for electric generators.
Related Topics
Fleming's Left-Hand Rule and Fleming's Right-Hand Rule . 
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