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State Fleming's Left Hand Rule

Last updated date: 15th Jul 2024
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The Rule

There is no electric field near a long, straight-thin uniform current-carrying conductor. Therefore, a charged particle moving parallel to the conductor experiences a magnetic force, as per the electrodynamics. The left hand Fleming rule came into existence through John Ambrose Fleming in the 19th Century. It was the simplest approach to understand the direction of the motion or the direction of the electric current. The left-hand rule of Fleming states that when we stretch the forefinger and middle finger of the left hand in a manner that they are mutually perpendicular to each other. 

Now, if the forefinger is taken as the direction of the current and the middle finger towards the magnetic field then the thumb points towards the motion of the conductor or the force. It is one of the rules of electricity. The reason being when a current-carrying the conductor comes under the magnetic field there is likely to be a force acting on the conductor. With the help of Fleming's left-hand rule, the director of the force can be determined. 

Usage of The Rule

Generally, Fleming's left-hand rule is used for electric motors. On the other hand, for electric generator the right-hand rule is applicable. The reason why the left-hand rule of Fleming is used in the electric motor because in the electric motor there is the presence of magnetic field and electric current which leads to the force that enables creating the motion. This can be referred to as the effect. Hence, the left-hand rule is used. It thus gives us the direction of the force that works on the current if well aware of the magnetic field. 

There is a need for different hands for motors and generators because there is a certain amount of difference between the effect and the cause. To elaborate that, the magnetic field and the electric current creates the force which results in motion and that is why the left hand is used. While the motion and the magnetic field exist in the electric generator and they create the current which is why the right hand is used. The physical basis for the rules that are to be remembered is that the electrons flow in the same direction from where they generate a cylindrical magnetic field that encircles around the conductor. 

Understanding Fleming’s Rule with Maxwell’s Corkscrew Rule

However, if a conductor is brought under the magnetic field forcefully there is supposed to be an induced current in that conductor. In such cases, the direction of the force would be determined by the implication of the Right-Hand rule of Fleming. It is to keep in mind that there is a relation between the current, force, and magnetic field which can be understood only with the implication of this Right Hand and Left-Hand rule. They help in showing the direction of any of these three parameters when the directions of the other two parameters are already identified. One magnetic field is induced around the conductor when current flows through it. They can be considered as the “m” where it is equal to the numbers of closed magnetic lines of force encircling the conductor. The direction of these magnetic lines can be understood by Maxwell's corkscrew rule or to say the grip rule of the right hand.

But in case of Fleming's left-hand rule consider a simple electromagnet that consists of only one circular loop of current wherein the current should flow in a clockwise direction. Now, imagine that straight horizontal conduct is kept in front of this loop wherein the current is flowing from the right direction to the left direction. By this, it can be understood that the current is flowing from the left to the right in the horizontal conductor. 

Now, divide the loop into two parts equally into upper and lower in comparison to the particular straight conductor. Next, consider an electron point A of that conductor. Now, as the current is flowing from right to left direction in that particular conductor, the electron at point A moves from left to right. The electron at A then experiences some force downwards which is similar in the case of all moving electrons also experience the force downwards. The electron pushes the whole conductor downwards with a similar force. This is the reason why the wire will tend to move downward.

In the third-hand rule, the thumb indicates the direction of the thrust or motion of the conductor. On the other hand, the forefinger represents the magnetic field's direction and the central finger indicates the direction of the current. This can be regarded as the first variant.