Fleming’s Rule-Coefficient of Coupling

Fleming’s rules are proposed by Sir John Ambrose Fleming, an English engineer, and physicist. He made great contributions to photometry, wireless telegraphy, electric and electronic measurements. He proposed the two most important magnetism principles known as Fleming’s left-hand rule and Fleming’s right-hand rule. The left-hand law states that the acting force is induced in the conductor when a charge carrying a conducting object comes in a magnetic field. So, the left-hand rule is used to determine the direction of the force. So, go thoroughly through the notes to better understand the Fleming left-hand rule and coefficient of coupling. We will also discuss the right-hand thumb rule. 

What is Fleming’s left-hand rule?

The force acts on the current-carrying conductor object kept in the magnetic field. The Fleming left-hand rule is used to determine the direction of the force. It’s important to remember that these criteria do not determine the object’s magnitude; rather, they show the direction of the three factors (current, force, and magnetic field) when the directions of the other two factors are known. 

Demonstration of Fleming’s left-hand rule:

According to the theory of Fleming’s left-hand rule, “when we stretch our thumb, index finger, and middle finger so that, they create an angle of the 900 ( means, perpendicular to each other). The conducting object placed in a magnetic field feels the Magnetic force.

The directions are denoted as the following:-

• Thumb: Direction of the force (F)

• Index finger: Direction of the magnetic field (B)

• Middle finger: Direction of the current (I)

What is Fleming’s right-hand rule?

The Flemings right-hand rule says that “when the thumb, middle finger and the forefinger are kept mutually perpendicular to each other so, that they make 90° of angle with each other, then the direction of the magnetic field is denoted by the forefinger, direction of motion of conductor is denoted by the thumb, and the induced EMF is denoted by the middle finger “. 

The directions are denoted as the following:-

• Thumb: direction of motion of the conductor

• Index finger: Direction of the magnetic field (B)

• Middle finger: induced EMF (from + to −, the terminal with lower electric potential to the terminal with higher electric potential, as in a voltage source)

Applications of the Fleming Right-hand rule:

The electromagnetic induction principle governs the operation of an electric generator. The current was generated in the coil when the coil is rotated between the magnet, or the magnet is moved in and out of the coil, and Fleming’s right-hand rule yields the current direction.

Difference between left hand and right-hand thumb rule:

What is the Coefficient Of Coupling?

The coefficient of coupling among the two coils is the fraction of the magnetic flux that is generated by the electric current in a single coil which is linked to other coils.

Suppose we have two coils, coil P and coil Q; when the current passes through the first coil P, it generates the flux; the complete flux might not be linked with the second coupled coil Q. It happens due to the leakage of the flux by the fraction (k), and here the term k is known as the Coefficient Of Coupling.

k=1, when the flux produced by one coil (P) is completely linked with the other coil (Q), and thus the coils are said to be magnetically tightly coupled.

k=0, when the flux produced by one coil (P) does not link at all with the other coil (Q) and this is called magnetically isolated.

So the coefficient of coupling k has a value between 0 and 1, i.e. 0 < k < 1.

We can also find out the relation between the coefficient of coupling and the inductance of the coils.

This relation is given as below:

k=M/√L1L2

Where M is the mutual inductance of the coils

L1 is the self-inductance of the first coil,

L2 is the self-inductance of the second coil.

Conclusion:

In the above notes, we have studied the Coefficient of Coupling Fleming’s left and right-hand rules. When the magnetic field direction and current direction are known, Fleming’s Left-Hand Rule is a simple and accurate approach to find the conductor’s direction of motion/force in an electric motor. The forefinger, middle finger, then thumb of our left hand are stretched perpendicular to each other in the following manner:

• Thrust or force on the conductor is indicated by the thumb.

• The forefinger shows the direction of the Magnetic Field.

• The current direction is indicated by the centre (middle) finger.

• In an electric motor, the left-hand rule determines the direction of motion.