Magnetic Flux – Magnetic Induction

Magnetic induction is also referred to as electromagnetic induction. What is the meaning of induction? The dictionary states, “the electric phenomena where electromotive force is generated due to change in the flow of current”. When an electric current is produced with the help of magnetic processes, it is called magnetic induction. The renowned British scientist Michael Faraday discovered the phenomenon of magnetic induction in the year 1831. Initially, scientists worldwide refused to give due recognition to Faraday’s achievements. Today, his principle of magnetic induction is used in so many modern machines, which transformed human lives. 

What was Faraday’s experiment?

Faraday used four simple tools and equipment for this experiment – A bar magnet, a galvanometer (an instrument that can measure the flow of a small amount of electric current in a circuit), a set of coiled wires, and a pair of electrical wires. 

He created an electric circuit by connecting the coiled wire with the galvanometer using a pair of wires. Then he moved the bar magnet towards the coiled wire. During this movement, he discovered that electric current was produced in the coiled wire, which could be detected by the deflection in the galvanometer. 

A similar effect could be observed as he pulled the magnet away from the coil. Again, the galvanometer could detect the flow of current in the coil. However, if the magnet was kept in a stationary position near the coil, there was no flow of electric current in the circuit. 

Thus, he concluded from this experiment that a change in the magnetic field near an electric conductor induces an electric current.

Significance of Faraday’s discovery of magnetic induction

This discovery was highly significant for two reasons:

1. Before this experiment, scientists discovered that the flow of electric current or any moving charged particle could produce magnetic fields around its surface. Faraday was the first to establish that a moving magnetic field near an electric conductor can induce an electric current. 

2. Before this experiment, the only known source of electric current was chemical cells or batteries. This experiment revealed a new technique of getting electric current utilising the magnetic field. 

What are Faraday’s laws of magnetic induction?

Faraday’s law of magnetic induction is also known as the laws of electromagnetism.

Faraday’s first law states that when the magnetic field surrounding a coil of wire is changed, it will induce an electromotive force (EMF) within the coil. We all know EMF is the electric force that causes the flow of electric current within a circuit. 

Thus, Faraday concluded that if this coil of the wire is a part of a closed electric circuit, then the current will start flowing through it naturally. He referred to it as induced current. 

Faraday’s second law states that the value of the induced EMF depends on two factors:

1. The rate at which magnetic flux is changing near the coil, and

2. The number of turns present in the coil

How can we change the magnetic field near the coil? 

Faraday has given four possible suggestions for this: 

1. The magnet can be moved back and forth near the coil.

2. The coil can be moved back and forth near the magnetic field.

3. The coil can be rotated near the static bar magnet.

4. The coil area exposed to the magnetic field can be changed. 

What is Lenz’s law of magnetic induction?

Emil Lenz was a Russian physicist who made an interesting observation from Faraday’s experiment on electromagnetic induction, known as Lenz’s Law.

According to Lenz’s Law, the direction of flow of the induced current (in Faraday’s experiment) will be such that a new magnetic field is created, which will resist the existing dynamic magnetic field that caused the induced EMF.

In Faraday’s law of magnetic induction, there was no mention of the actual direction in which the induced current will flow. Hence, we can say Len’s law completed the theory of magnetic induction. 

Practical uses of magnetic induction 

Human beings widely use electrical devices, and many of these devices work on the principle of magnetic induction. Working principles of two such devices are discussed here:

• Electric motor

An electric motor is used in many machines and appliances – starting from water pumps to a small hairdryer. If you look inside an electric motor closely, you will find a rectangular coil placed within a magnetic field. 

When we switch on the motor, an electric current passes through the coil, and a continuous torque forces the coil to move in cyclic motion. This movement of the coil causes rotation of the shaft attached to the coil. Thus, electrical energy supplied to the motor gets converted into mechanical energy. 

• Electric induction oven

This kitchen appliance has gained a lot of popularity because it is easy to use. There is a coiled copper wire below the cooking surface of an induction oven. When an electric current passes through this coil, it can produce a dynamic magnetic field. 

Now, the utensils used on an induction oven are specially made up of conductive material like cast iron. Due to the changing magnetic field, electric current is induced. This electric current in the vessel causes heat generation, which actually helps to cook the food.

Other practical applications of magnetic induction can be found in transformers, generators, etc. 

Conclusion

Before wrapping up the topic of magnetic induction, let us have a quick look at some important points that you should remember:

• The process in which electric current is induced with the help of a changing magnetic field is known as electromagnetic induction.

• Magnetic induction was discovered by Michael Faraday. His analysis of the phenomenon is popularly known as Faraday’s Law of Induction. 

• Magnetic induction has led to the invention of many useful devices which are an integral part of daily lives like electric motors, electric transformers, generators, and many more.