Faraday's Law

Are you someone finding the concept of Electromagnetic Induction (EMI) difficult? It may be because you are not clear with your basics themselves. To understand EMI you first need to grasp the concept of Faraday's Laws on EMI. These laws were postulated by one of the greatest physicists of all time- Michale Faraday. Mastering these laws will make understanding EMI easier for you.  

Before we understand Faraday's Law, let us first understand what Electromagnetic Induction is. 

Electromagnetic Induction is a phenomenon that induces a current in the circuit. This happens due to the change in the magnetic field. The current in the wire is caused due to the movement of the wire in the magnetic field or a change in the strength of the magnetic field with passing time. Both these situations can result in the flow of current in the wire. 

Electromotive force is viewed as an amount of energy that induces a flow of current through a circuit. The electromotive motive force that is generated in a wire due to the change in the magnitude of current in a coupled coil is called “mutual inductance”.

Faraday's Law - Formula & Example

Faraday's Law of EMI “Electromagnetic Induction”, is also called the law of electromagnetism. This law explains the operational principle of electric generators, electric inductors, electrical transformers, and electric motors. It helps in understanding important points that lead to the Electromagnetic Induction or production of electricity. Faraday's Law is conducted to see the way magnetic fields change due to the flow of current in wires. 

This law was first projected in 1831 by a chemist and physicist “Michael Faraday”. Because of him, the law got its name. Faraday's Law is the outcome of the observations of the three main experiments that he had conducted. Through these experiments, he found the principle of Electromagnetic Induction. 

Faraday’s First Law

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The first law of Faraday’s Electromagnetic Induction explains that when a wire is kept in a field that experiences a constant change in its magnetic field, then an electromagnetic field is developed. This phenomenon of development of the electromagnetic field is called an induced emf. If it is a closed circuit, then a current also gets induced inside the circuit. It is called “Induced Current”.

Ways of Changing the Magnetic Field

There are four means to change the magnetic field in a circuit. 

• By rotation of the coil in relation to the magnet.

• By movement of the coil into the magnetic field or outside the magnetic field.

• By modifying the region of a coil that is kept in the magnetic field.

• By movement of a magnet in the direction of the coil or against the direction of the coil.

Faraday’s Second Law

Now let us understand the second law of Faraday. This is another law by Faraday on Electromagnetic Induction. The law explains that the emf induced in a conductor is equivalent to the rate at which the flux is linked to the circuit changes. Here, this flux is the product of the flux in the wire and the number of turns present in the wire. 

Faraday's Law Formula

Let us see how Faraday's Law was established. Let us first understand the terms:

Where,

\[\epsilon\] = the emf or electromotive force

\[\phi\] = the magnetic flux

N = the total number of turns in the coil

The rate at which the magnetic flux changes through the circuit is equal to the amount of the electromotive force (ε) developed in the circuit. The above statement can be written in the following equation: 

\[\epsilon = \frac{dt}{d \Phi}\]

The electromotive force or EMF is the difference in the potential developed across an “unloaded loop”. This happens when the resistance present in the circuit reaches a high level. As EMF and voltage, both are measured in voltage, so one can consider EMF as voltage too.

There is another important law that describes electromotive force, like Faraday's Law. 

Lenz's law was postulated in 1833 by Heinrich Lenz. Where Faraday's Law describes the amount of the EMF generated inside the circuit, Lenz's law tells about the direction of the flow of current in the circuit. The law explains that the direction of the current will be opposite to the direction of flux that produced it. In other words, the direction of any magnetic field generated by the “induced current” is opposite to the modification in the actual field.

Lenz's law comes to the same conclusion as made by Faraday's Law. The only difference is the (minus “-“ sign). This negative sign is an indication that the direction of the magnetic field and the direction of induced emf have opposite signs.

 \[\epsilon = -\frac{dt}{d \phi}\]

If there are N number of turns in the coil, then the total magnetic induction in a coil is represented as \[\epsilon = -N \frac{dt}{d \phi}\]

​Faraday’s Experiment

Relationship Between Induced EMF and Flux:

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In the first Faraday's Law, it was stated that when the total strength of the magnetic field changes, then only it induces a current in the circuit. This was proved by connecting an ammeter to the wire loop. This ammeter gets deflected with the movement of the magnet in the direction of the wire.

In Faraday's second experiment, it was stated that when the current passes through the iron rod, it makes it electromagnetic. He also observed that due to relative motion between the coil and the magnet, an induced electromagnetic force gets produced. 

• When the magnet rotates about the axis, then no EMF is produced whereas when the magnet rotates on its axis, then it produces induced EMF. When the magnet is stationary or fixed at its place, then no deflection was observed in the ammeter. 

• When the magnet moves close to the coil, the voltage that was measured rose to its peak. 

• When the magnet moves away from the wire, the amount of voltage generated is in the opposite direction of the loop.

The 3rd experiment was conducted and recorded. In this experiment, when the coil was stationary it produced no deflection in the galvanometer. Thus, induced current was generated in the coil. But, when the magnet moved far from the circuit, then the ammeter showed deflection away from the loop.

Applications of Faraday's Law

Below are Some of the Important Uses of Faraday's Law:

• Transformers and other electronic devices operate on the principle of Faraday's Law.

• The induction cooker also operates on the principle of mutual induction that is in turn based on Faraday's Law.

• Inducing an EMF into an electro-magnetic flowmeter helps in recording the speed of the flow of liquids.

• Faraday's Laws are also applied in many medical devices such as MRI scans, X-ray machines, CT scans, etc.

Fun Facts About the Inventor of Faraday's Law:

Faraday's Laws are known worldwide due to their wide scope of applications but seldom do people talk about their inventor - Michael Faraday. To increase your curiosity towards the topic we have included a few fun facts about him that are as follows:

• He was a self-taught Physicist because while growing up his parents could not afford formal education for him

• He is known as the “Father of Electricity” along with Nikola Tesla

• His laws on electromagnetism paved way for the mechanized age

• In 1820 he invented a motor with magnets and mercury

• He demonstrated for the first time the pull of magnetic force for which he used bar magnet and iron filings. Today this experiment is performed by many students across the world.

• He popularized various scientific terminologies such as anode, cathode, etc. 

• He is one of the rare scientists to have been featured on a currency - the United Kingdom'S £20 note

Conclusion:

After conducting the above experiments, Faraday reached the inference that if there is relative motion between a wire and a magnetic field, then the total amount of flux linkage in the coil changes. This change in flux generates a voltage in the coil.

The law also states that with the change in the magnetic flux with time, the EMF or electromotive force gets produced. 

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