- Fleming’s Left Hand Rule: This rule is defined as a method to determine the direction of force in an electric motor when a current-carrying conductor is placed in a magnetic field.
- Magnetic Field Interaction: When current flows through a conductor in a magnetic field, it creates another magnetic field, influencing the conductor’s movement according to these magnetic interactions.
- Fleming’s Right Hand Rule: This rule helps identify the direction of induced current when a conductor moves within a magnetic field, essential for understanding generator functions.
- Inventor Background: The left and right-hand rules were invented by John Ambrose Fleming in the late 19th century, providing foundational knowledge for electrical engineering.
- Application in Technology: Both of Fleming’s rules are crucial for designing and operating electric motors and generators, showing the practical application of electromagnetic theory in technology.
What are Fleming’s Left And Right Hand Rules?
When a current carrying conductor lies in an external magnetic field, the field can exert a force on the conductor. Fleming’s left-hand rule, also called the motor rule, gives the force direction when the directions of conventional current and magnetic flux density are known. The force is zero if the current is parallel to the field.
When a conductor moves across magnetic flux, charge separation produces an induced electromotive force. An induced current flows only if the conductor forms part of a closed circuit. Fleming’s right-hand rule gives the direction of conventional current for generator action.
Both rules relate three perpendicular directions: magnetic field, conventional current and force or motion. The left hand applies when current and field produce force. The right hand applies when motion through a field produces an electromotive force.
The rules give direction, not magnitude. If any two of the three directions are known and mutually perpendicular, the corresponding hand rule identifies the third.
Fleming’s left-hand rule is mainly used to explain force in electric motors. Fleming’s right-hand rule is mainly used to explain induced current in electric generators.
What is Fleming’s Left Hand Rule?
A straight current carrying conductor in a uniform magnetic field experiences a force on its moving charges. The resulting force on the conductor is perpendicular to both conventional current and magnetic flux density.
In the figure below, a conductor of active length L lies vertically in a uniform horizontal magnetic flux density B between the N and S poles. If current I flows through it, the force magnitude is F = BIL sin θ, where θ is the angle between current and field. For perpendicular current and field, sin θ = 1 and F = BIL.
Hold the left thumb, forefinger and second finger mutually perpendicular. Point the forefinger in the magnetic-field direction from N to S and the second finger in the conventional-current direction. The thumb then points in the force or motion direction.
Current in a straight conductor also produces a magnetic field around it. The field forms concentric circles centred on the conductor; it is not a set of physical strings.
Maxwell’s corkscrew rule or the right-hand grip rule gives the direction of this circular field.
Using the right-hand grip rule, the magnetic-field or flux direction is clockwise when conventional current flows away from the viewer and into the page.
When an external horizontal magnetic field is present, its flux density combines vectorially with the field produced by current in the conductor.
In the diagram, the external magnetic field points from the North pole to the South pole, from left to right.
The conductor’s circular field reinforces the external field on one side and opposes it on the other. This sketch is a useful field-line representation of the same force described by the vector relation F = IL × B.
The drawn field lines are therefore closer together above the conductor and farther apart below it for the stated directions.
Field lines show the direction and relative strength of a magnetic field; they are not material bands. The physical force comes from the external field acting on moving charge carriers, with the conductor transmitting that force through its structure.
For the current and field directions shown, the force on the conductor is downward. Reversing either current or field reverses the force; reversing both leaves the force direction unchanged.
Applying Fleming’s left-hand rule to the same current and field directions gives the downward force shown in the diagram.
What is Fleming’s Right Hand Rule?
Under Faraday’s law of electromagnetic induction, an electromotive force is induced when motion through a magnetic field changes the flux linkage of a conductor. If the conductor is part of a closed circuit, the electromotive force drives current. The relevant motion is the component that cuts across the field.
Fleming’s right-hand Rule gives the direction of this induced conventional current from the directions of field and motion.
Hold the right thumb, forefinger and second finger mutually perpendicular. Point the forefinger from N to S in the magnetic-field direction and the thumb in the conductor’s motion direction. The second finger then points in the direction of induced conventional current. If the circuit is open, it instead indicates the polarity of the induced electromotive force.
Who Invented The Left and Right Hand Thumb Rules?
British electrical engineer John Ambrose Fleming developed the left- and right-hand direction mnemonics in the late 19th century.
Fleming presented the rules as practical ways to distinguish motor action from generator action. They remain known as Fleming’s left and right-hand rule.
