Fleming’s Right-Hand Rule: Explanation and Applications

When a moving conductor is placed inside a magnetic field, current is induced in it as a result of the conductor’s motion, and the current induced in the conductor has a directional relationship with the direction of the force applied inside the magnetic field.. This relationship between these directions is provided by the Fleming right-hand rule.

State Fleming’s right hand rule:

A right hand is stretched so that the thumb, middle finger, and index finger form a 90-degree angle with each other. The thumb then represents the direction of motion or force (F), the middle finger the direction of current (I), and the index finger the direction of magnetic field (I) (B).

Fleming’s Right-Hand Rule

When a conductor such as a wire attached to a circuit moves through an external magnetic field, an electric current is induced in the wire due to Faraday’s law of induction. The Flemings Right-Hand rule is used to determine the direction of induced current. Fleming’s left hand rule and right-hand rule were given by British physicist John Ambrose Fleming in the late \({19^{{\rm{th}}}}\) century.
According to Fleming’s right-hand rule magnetic field, if the first three fingers of the right hand are stretched mutually perpendicular to each other such that the forefinger points in the direction of the magnetic field, the thumb points to the direction of motion of conductor, then the middle finger points to the direction of induced current.

Visualising Fleming’s Right-Hand Rule

Michael Faraday found that a voltage is generated by moving a conductor in a magnetic field (or varying the magnet field near a stationary conductor). This wire or conductor must be part of an electrical circuit. In the absence of a circuit, the positive charge and negative charge will accumulate at the two ends of the conductor. If the ends of this conductor are attached to, e.g., a bulb, the circuit is complete, and an electric current starts flowing in the circuit. The direction of the current can be found in Fleming’s Right-hand Rule magnetic field.
The right-hand rule is used to find the direction of current induced within the coils of an electric generator. So whenever a conductor is forcefully moved in an electromagnetic field, an emf gets induced across the conductor. If the conductor is provided with a closed path, the induced emf causes a current flow.

When a conducting rod is pushed through a powerful magnet, as given in the situation above, we can use Flemings right-hand rule to determine the direction of induced current. To do so, Stretch the thumb, forefinger, and middle finger of the right-hand perpendicular to each other. Suppose the thumb represents the direction of the conductor’s movement, which is upwards. In that case, the forefinger represents the direction of the magnetic field, which is North to South, then the middle finger gives the direction of the induced current, which comes out be towards the right.

Right-Hand Rule

This process, by which a changing magnetic field in a conductor induces a current in another conductor, is called electromagnetic induction. The induced current is the highest when the direction of motion of the coil is at right angles to the magnetic field. To learn how the fleming’s right-hand rule can be applied, Stretch the thumb, forefinger, and middle finger of the right hand so that they are perpendicular to each other, such that:
Thumb: The thumb shows the direction of motion of The conductor.
Centre( middle) finger: The centre finger shows the direction of the induced current.
Forefinger: The fore( index) finger indicates the direction of the Magnetic Field.

Applications of Fleming’s Right-Hand Rule

Electric generator: It works on the principle of electromagnetic induction. When a coil is rotated between the magnet or when the magnet is rotated in and out of the coil, the current is induced in the coil, and Fleming’s right-hand rule gives the current direction. To understand this rule, let us learn about the working of an Electric generator:
1. An electric generator consists of a rotating rectangular coil \(ABCD\) placed between the two poles of a permanent magnet.
2. The two rings \(R1\) and \(R2\) are connected to the two ends of this coil. The inner side of these rings is made insulated, and these rings \(R1\) and \(R2\) are internally attached to an axle. The axle may be mechanically rotated from outside to rotate the coil inside the magnetic field. The two conducting stationary brushes \(B1\) and \(B2,\) are kept pressed separately on \(R1\) and \(R2,\) respectively.

3. The outer ends of the two brushes are connected to the galvanometer to show the flow of current in the given external circuit and when the axle attached to the two rings is rotated such that the arm \(AB\) moves up (and the arm \(CD\) moves down) in the magnetic field produced by the permanent magnet.
4. Let us say the coil \(ABCD\) is rotated clockwise. By applying Fleming’s right-hand rule, the induced currents are set up in these arms along with the directions \(AB\) and \(CD.\) Thus, an induced current flows in the direction of \(ABCD.\)
5. If there are larger numbers of turns in the coil, the current generated in each turn adds up to give a large current through the coil. This means that the current in the external circuit flows from \(B2\) to \(B1.\)
6. After half a rotation, arm \(CD\) starts moving up and \(AB\) moves down. As a result, the directions of the induced currents in both the arms change, giving rise to the net induced current in the direction \(DCBA.\)
7. The current in the external circuit now flows from \(B1\) to \(B2.\) Thus after every half rotation, the polarity of the current in the respective arms changes. Such a current, which changes direction after equal intervals of time, is called an alternating current. This device is called an \(AC\) generator.

Summary

When a conductor such as a wire attached to a circuit moves through an external magnetic field, an electric current is induced in the wire due to Faraday’s law of induction. According to Fleming’s right-hand rule, if the first three fingers of the right hand are stretched mutually perpendicular to each other such that the forefinger points in the direction of the magnetic field, the thumb points to the direction of motion of conductor, then the middle finger points to the direction of induced current. The right-hand rule is used to find the direction of current induced within the coils of an electric generator.

FAQs

Q.1: What is Faraday’s law of electromagnetic induction?
Ans: According to Faraday’s law of electromagnetic induction, whenever magnetic flux changes through a conducting loop, an electromotive force is induced in it.

Q.2: Explain Fleming’s Right-hand rule briefly.
Ans: According to Fleming’s Right-Hand rule, “Hold out the right hand with the first finger, second finger, and thumb at the right angle to each other. If forefinger represents the direction of the line of force, the thumb points in the direction of motion or applied force, then second finger points in the direction of the induced current”.

Q.3: State the principle of an electric generator.
Ans: An AC generator works on electromagnetic induction, which states that an induced current is produced when a moving conductor is placed inside a magnetic field.

Q.4: Explain the working of an AC generator briefly.
Ans: The \(AC\) generator consists of a coil \(ABCD\) connected to a galvanometer through slip rings. The galvanometer detects the current. If the coil is rotated anticlockwise, then arm \(AB\) of the coil moves downward arm \(CD\) of the coil moves upwards. Fleming’s Right Hand Rule gives the direction of induced current in these arms.

Q.5: How do we find the direction of induced current in a conductor moving through a magnetic field?
Ans: The direction of induced current can be determined by using Fleming’s Right-Hand Rule. According to this rule, if we held out the right hand with the first finger, second finger, and thumb at the right angle to each other, and If the forefinger represents the direction of the line of force, the thumb points in the direction of motion or applied force, then second finger points in the direction of the induced current.

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