Electromagnetic Induction is the only efficient way to generate electricity if we exclude solar panels. From generation of electricity till its distribution to user’s end, it has its application everywhere. This post will discuss about Electromagnetic Induction, Theory based on Faraday’s laws and Lenz’s law, various applications, advantages and disadvantages.

What is Electromagnetic Induction

Electromagnetic Induction is a process in which an Electro-Motive Force (Voltage) is produced across an Electrical Conductor with varying Magnetic Fields or Magnetic Flux. The theory of Electromagnetic Induction was discovered by Michael Faraday in the year 1830.

Introduction to Electromagnetic Induction

Fig. 1 – Introduction to Electromagnetic Induction

In the early decades of the nineteenth century, experiments based on Electric Current and Magnetism by many scientists proved that Electric Current and Magnetism are inter related. Michael Faraday and Joseph Henry discovered the fact that magnetic fields are produced by moving electrical charges.

The principle of Electromagnetic Induction has led to the development of modern day generators and transformers. The generation of Electromagnetic Induction can be achieved using two methods namely,

  • Electrical Conductor is placed in a moving Magnetic Field
  • Electrical Conductor is steadily moving within a Static Magnetic Field

Electromagnetic Induction Theory

Electromagnetic Induction Theory is based on the experiments conducted by Michael Faraday, Joseph Henry and Heinrich Friedrich Lenz and their deduced rules came to be known as :

  1. Faraday’s Laws of Electromagnetic Induction
  2. Lenz’s Law of Electromagnetic Induction

1. Faraday’s Laws of Electromagnetic Induction

The law states that ” The rate of change of magnetic flux with Time through the circuit is equal to the magnitude of the induced EMF in a circuit “.

Faraday conducted several experiments and was successful in proving that an EMF (Electro Motive Force) is induced in a coil when Magnetic Flux through the coil changes with Time. The Magnetic Flux around the conductor helps to determine the induced current called as “Eddy” current.

Mathematically, the induced EMF is derived by the equation:

The negative sign indicates the direction of ε and hence the direction of current in a circuit. The induced EMF can be increased by increasing the number of loops ‘N’ of a coil. The flux can be modified by changing the shape of a coil either by shrinking it or stretching it in a magnetic field. Rotating a coil in a magnetic field also induces EMF in the respective coils.

Illustration of Faraday's Laws

Fig. 2 – Illustration of Faraday’s Laws of Electromagnetic Induction

The above Fig. shows the illustration of Faraday’s Laws. Fig. 2(a) shows a coil C1 is connected to a galvanometer G and the North-Pole of a Bar Magnet is moving towards the coil. The galvanometer deflects indicating the presence of electric current in the coil and the galvanometer does not show any deflection when the magnet is stationary.

Similarly, when the magnet is withdrawn from the coil, the galvanometer shows deflection in the opposite direction which indicates that the current is flowing in the reverse direction.

Faraday also observed that when the magnet is moved towards or pulled away from the coil faster, the deflection in the galvanometer is larger. This experiment proved that the relative motion between the magnet and the coil generates current in the coil.

Fig. 2(b) shows C1 coil connected to galvanometer and second coil C2 connected to a battery and the current in the coil C2 produces a steady magnetic field. As coil C2 moves towards C1, the galvanometer shows deflection indicating the current in coil C1.

Similarly, when C2 is moved away from C1, the deflection points in the opposite direction indicating reverse flow of current. This experiment also proved that the relative motion between the coils could induce electric current.

In the last experiment, illustrated in Fig. 2(c) he connected coils C1 and C2 to galvanometer and battery respectively and held the coils at Stationary position and the galvanometer showed momentary deflection when the key (K) is pressed. No deflection was found when the key was pressed continuously. The galvanometer showed reverse deflection when the key was released. Thus Faraday proved that the relative motion was not an absolute requirement.

2. Lenz’s Law of Electromagnetic Induction

The law states that “The polarity of the induced EMF is such that it tends to produce a current which opposes the change in magnetic flux that produced it”.

Mathematically, the induced EMF and the current is given by the equation:

Consider the Fig 3, where the North-Pole of a Bar Magnet is being pushed towards the closed coil and the Magnetic Flux through the coil increases. Current is induced in the coil in a direction opposite to the increase in Magnetic Flux. Similarly, if the North Pole of the magnet is moved away from the coil, the magnetic flux through the coil decreases. A repulsive force is experienced by the Bar Magnet due to the induced current.

Illustration of Lenz's Law

Fig. 3 – Illustration of Lenz’s Law

Applications of Electromagnetic Induction

The applications of Electromagnetic Induction are:

  • Generators
  • Transformers
  • Credit/Debit Card Readers (explained below)
  • Induction Cook tops (explained below)
  • Electrical Motors and Inductors
  • Wireless Charging

Electronic Card Swiping System Based on Electromagnetic Induction

Electronic card swiping machine or card reader machine is based on the principle of Electromagnetic Induction. Any Credit/Debit card has a magnetic strip on the reverse side of the card called Magstripe. The Magstripe is made up of very small magnetic particles (20 millionths of an inch) and they are aligned in North-South direction. Hence the entire magnetic stripe acts as a Bar Magnet where one end is a North Pole and the other end is a South Pole.

Electronic Card Swiping System Based on Electromagnetic Induction Theory

Fig. 4 – Electronic Card Swiping System Based on Electromagnetic Induction Theory

The magnetic stripe (Magstripe) which has varying magnetic field orientations along the length of the card is swiped through a card reader, a change in Magnetic Flux is produced in one direction. This creates potential difference as the card which has varying magnetic fields is passed through a card reader which is a Pick Up Coil acting as a closed loop.

When the card is swiped past the magnetic head on the card swiping machine, current is produced which triggers the information access stored in the respective Registers. According to Michael Faraday, changing magnetic field induces an electrical field.

Induction Cook Top System Based on Electromagnetic Induction Theory

In Induction Cook top, magnetic field is produced when the appliance is turned on and the current is passed through the copper coil. Copper coil acts as a conductor. The electric current passing through the coil generates a magnetic field in all directions around the coil.

Devices Using Electromagnetic Induction Principle1 (1)

Fig. 5 – Induction Cook Top System Based on Electromagnetic Induction Theory

When a cooking utensil is placed on the cook top, the magnetic field produced by the coil pass through the utensil. This varying magnetic field causes flow of electric current. This induced current dissipates some of its energy in the form of heat which increases the temperature of the utensil placed on the cook top and food gets cooked by the heat that was transmitted.

Advantages of Electromagnetic Induction

The advantages of Electromagnetic Induction are:

  • AC or DC electrical power can be generated using Electromagnetic energy source
  • Eliminates the need of an external electrical source to generate electrical power

Disadvantage of Electromagnetic Induction

The electromagnetic fields generated to produce electricity can be dangerous under certain circumstances

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