Introduction to Fleming's Left Hand Rule and Fleming's Right Hand Rule
When a current-carrying conductor is kept in a magnetic field, a force applies on it; the direction of this force can be determined using Fleming's Left-Hand Rule. Similarly, if a moving conductor is placed in a magnetic field, an electric current will be induced in it. The direction of the induced current can be determined using Fleming's Right-Hand Rule.
It's vital to note that these rules don't define magnitude; rather, they demonstrate the direction of the three parameters (magnetic field, current, and force) when the other two parameters' directions are known. Electric motors are predominantly affected by Fleming's Left-Hand Rule, while electric generators are primarily affected by Fleming's Right-Hand Rule.
Fleming’s Left-hand Rule and Fleming’s Right-hand Rule
Fleming’s Left-hand Rule
Fleming’s left- hand rule states that if we stretch the thumb, middle finger and the
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.
Then the direction for each finger is represented as follows:
Thumb: It points towards the direction of force (F)
Middle finger: It represents the direction of the current (I)
Index finger: It represents the direction of the magnetic field (B)
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Fleming’s Right - hand Rule
Fleming's Right hand 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.
Then the direction for each finger is represented as follows:
Thumb: It is along the direction of motion of the conductor.
Middle finger: It points in the direction of the induced current.
Index finger: It points in the direction of the magnetic field.
The representation for right-hand rule is as follows:
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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
Fleming’s Left-hand Rule Application: Working of an Electric Motor
Theory behind Fleming’s left-hand rule: 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, like we see in the image below:
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Working of an Electric Motor
Let's take a rectangular current carrying loop and put it inside the magnetic field as shown below:
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Here, in the above diagram of the electric motor, we notice that each side of the loop behaves as a current-carrying conductor.
Also, 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 the magnetic field, these 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 to determine the direction of the force and the magnetic field:
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Now, let us apply Fleming’s left-hand 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 would the loop rotate?
Additionally, in an orange wire, the current is flowing in the right direction while magnetic field B is in the left direction. The flow of current and the magnetic field are in the opposite direction.
So, if the magnetic field B is parallel to the orange wire, no force would act upon it, so how will the loop rotate? It’s because forces acting in opposite directions make the loop rotate. Now, let us understand how.
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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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Here, in fig. 5, we notice that though forces are in opposite directions, their direction doesn’t change. Also the orange wire is not parallel, and it makes some angle with the magnetic field lines, which is why the loop rotates.
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 inward wire 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, as the loop rotates again in the following manner (Fig. 7), the problem arises that again the forces are in opposite directions, first, it will slow then it would start rotating in an anticlockwise direction: like this:
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As soon as the rotation starts, the wire will get distorted like this:
Now, in place of changing the direction of the magnetic field, we change the direction of current by attaching a battery with the wire and we notice that as the rotation starts, the wire will distorts in the following manner:
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However, the above process would continue and won't allow a complete rotation in one direction.
To resolve this issue, we use the commutator and a carbon brush for a complete rotation of the loop to avoid distortion in the wire, as we can see in Fig. 8 above.
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.
A 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.
After we have connected the communicator to the arrangement, we notice that after a half rotation, the position of the split ring position changes in the following manner (Fig. 9), the terminals of the battery connected across the split rings are also changing and helps change the direction of the current in the following figure. 9:
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 moto
Hence, our issue was resolved by using a commutator for the smooth rotation of the motor.
So, we learnt that we use Fleming's left-hand rule for the smooth functioning of electric motors. This reason makes this rule a renowned application of electric devices.
Solved Example on Magnetic Field in a Current-Carrying Conductor
Let's take a conductor placed in a magnetic field:
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Here, K L 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 L
B = F / I * K L
Unit of B = N/ A * m.
S.I. unit of I is A
S.I unit of k L is m.
and for B, it is Tesla.
1 Tesla = 1 N / Am
Concept Bases Questions:
1. 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.
Solution:
Given: I = 5A, L = 4m, and B = 3 T
Since, F = I * B * L
= 5 * 3 * 4
F = 60 N
Thus, the force produced is 60 N.
2. 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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Solution:
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.
3. A current-carrying conductor does not tend to rotate in a magnetic field. Why does this happen?
It means, no force is acting on the current-carrying conductor due to the magnetic field, which means that the current-carrying wire is parallel to the magnetic field.
4. Is the source of the magnetic field analogous to the source of electric current?
No, it’s because the source of the magnetic field is not a magnetic charge. However, in the case of the electric field, the source of the electric field is an electric charge.
