Fleming's Left Hand Rule Explained with Formula, Diagram and Applications

Fleming's left hand rule is a simple method used to find the direction of force acting on a current-carrying conductor placed in a magnetic field. It is widely used to explain the working of electric motors and helps students easily remember the relationship between force, magnetic field, and electric current.

Why does the rotor inside an electric motor start rotating when electricity flows through it? The answer lies in Fleming's left hand rule. This article explains its definition, diagram, working, applications, and importance in simple language.

Table of Contents

• Who Invented Fleming's Left Hand Rule
• Fleming's Left Hand Rule Explained with Diagram
• Force Formula of Fleming's Left Hand Rule
• Fleming's Left Hand Rule in Electric Motors
• Advantages and Disadvantages of Fleming's Left Hand Rule
• Real-Life Applications of Fleming's Left Hand Rule
• Frequently Asked Questions on Fleming's Left Hand Rule

Who Invented Fleming's Left Hand Rule 

Fleming's left hand rule was introduced in the late 19th century by John Ambrose Fleming. He developed this rule to help explain the relationship between the direction of force, magnetic field, and electric current in electric motors.

Before this rule was introduced, it was not easy to determine the direction of motion produced when a current-carrying conductor was placed in a magnetic field. Fleming's left hand rule provided a simple method that engineers and students could easily remember.

Later, John Ambrose Fleming introduced Fleming's right hand rule, which is used to find the direction of the induced current in electric generators, while the left-hand rule is used for electric motors.

Fleming's Left Hand Rule Explained with Diagram 

Fleming's left hand rule is used to find the direction of the force acting on a current-carrying conductor placed in a magnetic field. The rule uses the thumb, forefinger, and middle finger of the left hand, held so that they are at right angles (90°) to each other as shown in figure which is given below, .

Each finger represents a different quantity:

• Thumb: Direction of the force or motion
• Forefinger (Index Finger): Direction of the magnetic field
• Middle Finger: Direction of the electric current

So we can state Fleming's left hand rule, 

“If the thumb, forefinger, and middle finger of the left hand are held perpendicular to one another, then: The thumb points in the direction of the force or motion. The forefinger points in the direction of the magnetic field. The middle finger points in the direction of the electric current.”

Interestingly! If you know the directions of the magnetic field and electric current, this rule helps you easily find the direction in which the conductor will move.

Force Formula of Fleming's Left Hand Rule

Now you may ask, can the force acting on a conductor also be calculated?

Yes. The force on a current-carrying conductor placed in a magnetic field is calculated using the following formula:

F=BIL

Where, 

• F is the force acting on the conductor (Newton, N)
• B is the magnetic field strength (Tesla, T)
• I is the electric current (Ampere, A)
• L is the length of the conductor inside the magnetic field (metre, m)

The formula shows that the force increases when the magnetic field, current, or length of the conductor increases.

Fleming's Left Hand Rule in Electric Motors

An electric motor converts electrical energy into mechanical energy. This happens because a current-carrying conductor placed in a magnetic field experiences a force. Fleming's left hand rule is used to determine the direction of this force and the resulting motion of the conductor.

Have you ever wondered why the rotor inside a motor starts rotating?

When electric current flows through the wire coils of the motor, it creates a magnetic field around the conductor. This magnetic field interacts with the magnetic field produced by the permanent magnets or electromagnets inside the motor. As a result, a force is generated, causing the rotor to rotate.

Interestingly! If the direction of the current or the magnetic field changes, the direction of the force also changes. This principle is used to control the rotation of electric motors.

The fact is that this rule is not limited to just one type of motor. It is used to explain the basic working principle of many motors, including,

• DC motors
• AC motors
• Brushed motors
• Brushless motors
• Induction motors

These motors work on the same basic idea: a current-carrying conductor placed in a magnetic field experiences a force, and Fleming's left hand rule helps determine the direction of that force.

Advantages and Disadvantages of Fleming's Left Hand Rule

Like every scientific principle, Fleming's left hand rule has both advantages and limitations. It provides a simple way to determine the direction of force on a current-carrying conductor, but its use is limited to specific situations involving electric motors. 

The rule offers several benefits, such as,

• It helps predict the direction of force quickly and accurately.
• It makes the working of electric motors easier to understand.
• It is simple to remember using three fingers of the left hand.
• It helps engineers design efficient electric motors.
• It is useful for learning the basics of electromagnetism.

This rule also has certain limitations.

• It is mainly used for electric motors.
• It cannot be applied to every electromagnetic situation.
• It only shows the direction of the force, not its magnitude.
• It may not fully explain complex motor designs

Real-Life Applications of Fleming's Left Hand Rule

Fleming's left hand rule is used in many electrical devices where a current-carrying conductor moves in a magnetic field. Some common applications are:

• Explaining the working of electric motors.
• Finding the direction of force on a conductor.
• Designing DC and AC motors.
• Studying electromagnetism in physics.
• Developing electrical machines used in industries.

Fleming's left hand rule helps determine the direction of force acting on a current-carrying conductor in a magnetic field. We also covered who introduced the rule, how to state Fleming's left hand rule, its formula, working in electric motors, advantages, limitations, and its real-life applications. This simple rule makes it easier to understand the basic principle behind many electrical machines.