Fleming's Left Hand Rule and Right Hand Rule

Introduction

Fleming’s Left-hand Rule

Fleming’s left - hand rule states that if we stretch the thumb, middle finger and the index finger of the left hand in such a way that they make an angle of 90 degrees(Perpendicular to each other) and the conductor placed in the magnetic field experiences Magnetic force.

Such that:

  1.  Thumb: It points towards the direction of force (F)

  2. Middle Finger: It represents the direction of the current (I)

  3. Index Finger:  It represents the direction of the magnetic field (B)           

Fig.A: Fleming’s Left-hand Rule

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Fleming’s Right - hand Rule

This rule states that if we stretch the thumb,  middle finger, and an index 

finger in such a way that they are mutually perpendicular to each other. 

Such that:

1. Thumb: It is along the direction of motion of the conductor.

2. Middle Finger: It points in the direction of the induced current.

3. Index Finger:  It points in the direction of the magnetic field.

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Fig.B: Fleming’s right-hand rule 

On this page, we shall learn the following things: 

  • Fleming’s left- hand rule

  • Fleming’s left- hand rule application

  • Fleming’s right-hand rule

  • Difference between Fleming’s left-hand and fleming’s right-hand rule

What is Fleming’s Left-hand Rule?

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Here, When current flows through a conducting wire, and an external magnetic field is applied across that flow, the conducting wire experiences a force orthogonal both to that field and direction of the current flow.

Application of Fleming’s left hand rule:

 Electric motor using Fleming's left-hand rule

Let's take a rectangular current carrying loop and put it inside the magnetic field as shown below:

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Each side of the loop behaves as a current-carrying conductor.

The direction of force is different at each side of this conductor, and that force is acting on that conductor due to the production of magnetic field, this magnetic field lines would make varying forces at each side, and the direction of the force at each side of this loop can be determined by using Fleming’s left-hand rule, and electricity changes to the rotatory motion.

Now look at the pink wire, and observe the direction of the current in the same. In order to determine the direction of the force and the magnetic field: 

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Now apply the same rule for the blue wire:

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As soon we applied Fleming’s left-hand rule:

We can see the direction of the Force and magnetic field in Fig.3

In pink wire: The force is acting ‘upwards.’

In blue wire: The force is acting ‘downwards.’

But one thing we can see in orange wire, the current is flowing in the right direction while magnetic field B is in the left direction. The current and magnetic field is in the opposite direction.

The magnetic field B is parallel to the orange wire, hence no force would act upon it. How the loop would rotate?

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In Fig.4, we can see that forces are in opposite directions and the loop starts rotating in a clockwise direction.

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The direction of force is not changed, the orange wire is not parallel, and making an angle with the magnetic field lines, and now applying fleming’s left-hand rule here: we get like this: 

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Force in the lower orange wire is outwards, and that of the upper orange wire in inwards.

The orange wires would try to distort the loop, as the loop is of very high strength and the spinning of the loop won’t be there at this moment. Here, we would consider these two forces as negligible.

Now, again loop rotates like this:

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Now the problem arises that again the forces are in opposite directions, first, it will slow then it would start rotating in anticlockwise direction: like this:

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This process would continue and won't allow a complete rotation in one direction.

In place of changing the direction of the magnetic field, we can change the direction of current by attaching a battery with the wire: like this:

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As soon as the rotation starts, the wire will get distorted like this:

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Now what we can do is use the commutator and a carbon brush for a complete rotation of the loop without getting the wire distorted.

Here,  Commutator is a split ring with two metallic halves.

Carbon brushes are just touching the Commutator and are linked with wire, so that if the current reaches the loop via 

these brushes.    

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Now after a half rotation, the position of split ring position changes like this:

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As we can see the terminals of the battery connected across the split rings are also changing and would help in changing the direction of the current as well.

This is how an electric motor would make a complete rotation.

So this is how fleming’s left-hand rule is applied to an electric motor.

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Summary :

1. Let's take a conductor placed in

a Magnetic Field:

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Here, K being the length of the current-carrying conductor (rod),  F is the force and the B be the magnetic field, then:

F = I * B * K

B = F / I * K

B = N/ A * m.

S.I. unit of I is A

S.I. unit of k is m.

and for B, it is Tesla.

Tesla = N / Am

Concept Bases Questions:

Q1: Let's say the current flowing the conductor is 5 A, length of the rod be 4m and the magnetic field generated by 3 T. Find the force produced.

Ans:

Given: I = 5A, K = 4m, and B = 3 T

Since, F = I * B * K

               = 5 * 3 * 4

            F = 60 N

Thus, the force produced is 60N.

Q2: An electric current is moving from right to left in the wire. Which way does the induced magnetic field point to the location of the triangle?

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Ans: Applying Fleming’s left-hand rule: Rotating your middle finger in the direction of an electric current that is in the right direction, we get that the force is pointing inwards and the direction of the magnetic field is downwards that is into the screen.

Q3: A current-carrying conductor does not tend to rotate in a magnetic field. Why does this happen?

Ans:  It means, no force is acting on the current-carrying conductor due to the magnetic field, which viable that current-carrying wire is parallel to the magnetic field.                        

Q4: Is the source of the magnetic field analogous to the source of electric current?     

Ans: No, because the source of the magnetic field is not a magnetic charge, but in the case of the electric field, the source of the electric field is an electric charge.