- Faraday’s Law Definition: Faraday’s law of electromagnetic induction is defined as the principle that a changing magnetic field within an electric circuit produces an electromotive force.
- First Law: Faraday’s first law states that any change in the magnetic environment of a coil induces an EMF, known as induced EMF, and, if the circuit is closed, induces current as well.
- Second Law: Faraday’s second law clarifies that the induced EMF’s magnitude equals the rate at which the magnetic flux linkage through the coil changes.
- Enhancing EMF: Increasing the coil’s number of turns, the magnetic field strength, or the relative motion speed between the coil and the magnet can amplify the induced EMF.
- Applications and Impact: The faraday law of electromagnetic induction underpins the functionality of transformers, generators, and even musical instruments, demonstrating its broad influence in both technology and culture.
What is Faraday’s Law
Faraday’s law of electromagnetic induction (referred to as Faraday’s law) is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF). This phenomenon is known as electromagnetic induction.
Faraday’s law states that a current will be induced in a conductor which is exposed to a changing magnetic field. Lenz’s law of electromagnetic induction states that the direction of this induced current will be such that the magnetic field created by the induced current opposes the initial changing magnetic field which produced it. The direction of this current flow can be determined using Fleming’s right-hand rule.
Faraday’s law of induction clarifies how devices like transformers, motors, generators, and inductors function. Named after Michael Faraday, this law emerged from his experiments with a magnet and a coil, revealing that changes in magnetic flux through the coil induce an EMF.
Faraday’s Experiment
In this experiment, Faraday takes a magnet and a coil and connects a galvanometer across the coil. At starting, the magnet is at rest, so there is no deflection in the galvanometer i.e the needle of the galvanometer is at the center or zero position. When the magnet is moved towards the coil, the needle of the galvanometer deflects in one direction.
When the magnet remains stationary, the galvanometer’s needle returns to zero. As the magnet moves away from the coil, the needle deflects in the opposite direction, returning to zero when the magnet stops moving. Similarly, if the magnet is held stationary and the coil moves away, and towards the magnet, the galvanometer similarly shows deflection. It is also seen that the faster the change in the magnetic field, the greater will be the induced EMF or voltage in the coil.
| Position of magnet | Deflection in galvanometer |
| Magnet at rest | No deflection in the galvanometer |
| Magnet moves towards the coil | Deflection in galvanometer in one direction |
| Magnet is held stationary at same position (near the coil) | No deflection in the galvanometer |
| Magnet moves away from the coil | Deflection in galvanometer but in the opposite direction |
| Magnet is held stationary at the same position (away from the coil) | No deflection in the galvanometer |
Conclusion: From this experiment, Faraday concluded that whenever there is relative motion between a conductor and a magnetic field, the flux linkage with a coil changes and this change in flux induces a voltage across a coil.
Michael Faraday formulated two laws on the basis of the above experiments. These laws are called Faraday’s laws of electromagnetic induction.
Faraday’s First Law
Any change in the magnetic field of a coil of wire will cause an emf to be induced in the coil. This emf induced is called induced emf and if the conductor circuit is closed, the current will also circulate through the circuit and this current is called induced current.
Method to change the magnetic field:
- By moving a magnet towards or away from the coil
- By moving the coil into or out of the magnetic field
- By changing the area of a coil placed in the magnetic field
- By rotating the coil relative to the magnet
Faraday’s Second Law
It states that the magnitude of emf induced in the coil is equal to the rate of change of flux that linkages with the coil. The flux linkage of the coil is the product of the number of turns in the coil and flux associated with the coil.
Faraday Law Formula
Consider, a magnet is approaching towards a coil. Here we consider two instants at time T1 and time T2.
Flux linkage with the coil at time,
Flux linkage with the coil at time,
Change in flux linkage,
Let this change in flux linkage be,
So, the Change in flux linkage
Now the rate of change of flux linkage
Take derivative on right-hand side we will get
The rate of change of flux linkage
But according to Faraday’s law of electromagnetic induction, the rate of change of flux linkage is equal to induced emf.
Considering Lenz’s Law.
Where:
- Flux Φ in Wb = B.A
- B = magnetic field strength
- A = area of the coil
How To Increase EMF Induced in a Coil
- By increasing the number of turns in the coil i.e N, from the formulae derived above it is easily seen that if the number of turns in a coil is increased, the induced emf also gets increased.
- Increasing the magnetic field strength around the coil boosts the magnetic flux, thus enhancing the induced EMF. Theoretically, a stronger magnetic field means the coil intersects more lines of force, resulting in greater EMF.
- By increasing the speed of the relative motion between the coil and the magnet – If the relative speed between the coil and magnet is increased from its previous value, the coil will cut the lines of flux at a faster rate, so more induced emf would be produced.
Applications of Faraday’s Law
Faraday law is one of the most basic and important laws of electromagnetism. This law finds its application in most of the electrical machines, industries, and the medical field, etc.
- Power transformers function based on Faraday’s law
- The basic working principle of the electrical generator is Faraday’s law of mutual induction.
- Induction cookers, operating on mutual induction, rapidly heat food. They function by sending current through a copper coil beneath the cookware, inducing a magnetic field that generates heat via the current in the conductive container.
- Electromagnetic Flow Meter is used to measure the velocity of certain fluids. When a magnetic field is applied to an electrically insulated pipe in which conducting fluids are flowing, then according to Faraday’s law, an electromotive force is induced in it. This induced emf is proportional to the velocity of fluid flowing.
- Faraday’s concepts, particularly his lines of force, are fundamental to Maxwell’s electromagnetic equations. Faraday’s law illustrates how a changing magnetic field induces a change in the electric field, a principle integral to Maxwell’s theories.
- It is also used in musical instruments like an electric guitar, electric violin, etc.
