Visual Mnemonics Got Easier With Fleming’s Left-Hand Rule

Juliet D'cruz

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Understand Fleming’s left-hand rule with these visual mnemonics.

What is Fleming’s left-hand rule?

The left-hand rule by Fleming for electric engines is one example of visual mnemonics; the other is Fleming’s right-hand rule for the generators. It states that:

  • If the forefinger, the middle finger, and the thumb of the left hand are stretched at right angles mutually to one another,
  • Such that the forefinger points in the direction of the magnetic field B and the middle finger in the direction of the current I, 
  • Then the thumb will always point in the direction of the force F on the conductor.

At its centre, the left-hand rule is a visual mnemonics that utilises the thumb, the index, and the centre finger of the left hand. The hand is held with the palm up, the thumb and centre fingers adjusted like they were joined start to finish, and the fore-finger held out perpendicularly. The rubric for this standard is as per the following: 

Thumb: The thumb is a portrayal of the direction of thrust on the conductor. 

Index: Also known as the index finger, this addresses the course of the magnetic field. 

Center Finger: Also known as the middle finger, is illustrative of the course of the current.

Expression for the force: The current in a conductor joined to the poles of a battery is the drift of free electrons from the lower to the higher potential end of the conductor. When the conductor is put in a magnetic field, magnetic forces are imposed on the moving electrons within the conductor body. The final result of these microscopic forces is the total macroscopic force on the whole conductor.

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Let us consider a portion of length l and cross-sectional area A of a straight conductor carrying a current I. Let it be placed at right angles to a magnetic field B in the plane of the page directed downwards as in the figure.

Let n be the total number of free electrons per unit volume of the given conductor and Vd be the drift velocity of the electrons. From the relation F=qV ×B, the magnitude of the force on each electron is eVdB, where e is the negative charge on an electron. If, however, the conductor makes an angle θ with the magnetic field B measured from the conductor towards the field B, then the magnitude of the force on each electron is given by:


The total number of electrons in the length l of the conductor is:


The total force on the free electrons, and hence on the length l of the conductor is, therefore:

F=F’ ×N=(eVdBSinθ)(nAl)=(neAVd)BlSinθ.

But neAVd=I, the current in the conductor. Therefore,


In vector form, we can write as,

F=I L×B.

How Visual Mnemonics Got Easier with Fleming’s Left-hand rule?

Visual Mnemonics got easier with Fleming’s left-hand rule for motors. There are two sections to a standard DC electric engine: a rotor and a stator. The rotor is allowed to turn inside the stator since it homes into it. The stator of an essential engine is a ring of long-lasting magnets, while the rotor is conveniently wrapped with conductive copper wire on various occasions. 

The rotor is the main part that gets power from a different source. 

We should now investigate Fleming’s Left-Hand Rule- Electrical flow is sent through copper wire curls on the rotor from an outside power source. The electromagnetic field made by this connects with the magnetic field produced by the stator’s long-lasting magnets. 

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This interaction results in the generation of an actual power that is perpendicular to the fields. Due to how an electric engine is built (rotor inside stator), this physical force shows itself as rotor rotation.

We can improve the efficiency of the electric motor through-

  • An increasing number of turns.
  • Increasing the strength of the current.
  • By increasing an area of a cross-section of the coil.

We can simply understand how electric motors work with the help of Fleming’s left-hand rule. We can easily find out the direction of motion of electric motors with the help of Fleming’s Left-hand Rule.

Fleming’s Right-hand rule

As indicated by Faraday’s law of electromagnetic induction, when a moving conductor is put inside a magnetic field, a current will be instigated in it. On the chance when the conductor is powerfully moved inside the magnetic field, there will be a connection between the direction of applied force, magnetic field and the current. Fleming’s right-hand rule decides this connection between these three headings.

As displayed in the figure over, the right-hand rule expects you to-

“Hold the right-hand index finger, centre finger and thumb perpendicular to each other. On the off chance that the forefinger addresses the direction of the magnetic field, the thumb represents the direction of motion or applied force; then, at that point, the centre finger will point toward the initiated current.”

Difference between Fleming’s Left and Right-hand Rule:

  • Fleming’s left-hand rule is generally applied to electric motors, whereas Fleming’s right-hand rule is applied to electric generators.
  • In the left-hand rule, the motivation behind the rule is to discover the direction of motion in an electric motor, whereas In the right-hand rule, we are required to find out the direction of induced current in a magnetic field.
  • The thumb here indicates the direction of the force on the conductor in Fleming’s left-hand rule, while the thumb indicates the direction of motion of the conductor in Fleming’s right-hand rule.
  • The index finger here points in the direction of the magnetic field in the case of the left-hand rule, whereas the Index finger points the direction of the magnetic field in the right-hand rule as well.
  • The middle finger here points in the direction of current in the left-hand rule, whereas the right-hand rule also represents the direction of the induced current by a magnetic field.


This article highlights how visual mnemonics can be used to understand Fleming’s Left-Hand Rule. Now that you know all about the topic mentioned above, you can take up practice questions to excel and perform well in exams.