Electromotive Force (EMF)

EMF stands for electromotive force and it is a current produced in conductor through the magnetic field. EMF works according to the Faraday's first law of electromagnetic induction. When a moving conductor is placed between a magnetic field, a force is produced in the conductor named as electromotive force (EMF). EMF is also known as electric current which is the rate of change electric charge through any cross sectional area/conductor. Let's read about Faraday's law of electromagnetic induction.

Faraday’s law of Electromagnetic Induction

Faraday’s law of electromagnetic induction is about magnetic field and it proves that an emf is produced in a moving conductor when placed it in a magnetic field. Faraday’s law of electromagnetic induction is further divides into two laws:

Faraday’s First Law of Electromagnetic Induction

Faraday’s first law of electromagnetic induction states that “When a conductor cuts a magnetic flux, an EMF is induced in that conductor.” A Simple loop generator/loop generator is based on this law of electromagnetic induction.

Faraday’s Second Law of Electromagnetic Induction

Faraday’s second law of electromagnetic induction states that “The magnitude of generated EMF in a conductor(wire) is equal to the rate of change of flux linkage.”

The conversion of mechanical energy into electrical energy is based on the faraday’s first law of electromagnetic induction and this law is used in the construction of DC Generator. Without this law, DC Generator is not capable to convert mechanical energy to DC electrical energy.

How EMF is Induced?

Take a wire and it has a magnetic force in the magnetic field and there is no any resistor in free space. Bring the magnet close to the wire the magnetic force is equal and opposite on the protons and electrons in the space. The charge imbalance is built by pushing the electrons to the end of the wire. It act like a battery and due to magnetic field, emf is induced.

Measurement OF EMF

To measure the emf we use a device which is named as galvanometer. It is a very sensitive device and it measure a minor amount of current. Emf is the amount of current produced in a conductor or a coil. The procedure is given below:

Connect a coil of wire to the galvanometer
Bring the magnet close to the coil.
If the magnet is held constant on one position no current is flowed through the coil.
If the magnet is moving continuously near to the conductor or coil the needle of the galvanometer start deflecting and it means that current is flowing through the coil and EMF is induced in the conductor.

Note: The direction of the EMF produced in a conductor is according to the direction of the magnetic field.

Conclusion

The result is that a changing magnetic field will produce a voltage in a coil, that can cause a current to flow. If the magnetic flux near to a coil is changed an electric current will produce in a conductor. This current is called induced emf.

Formula to measure the magnetic flux

The formula to measure the magnetic flux is given below:

Φ = BAcosΦ

where B is the magnetic field, A is the area of a wire or conductor and Φ is the angle between magnetic field.

Ways to Induce EMF in Loop

The following are the ways to induce the emf in loop:

By changing the magnetic field.
By changing the area of the loop.
By changing the angle between the field and the loop.

Motional EMF

Suppose you have a metal rod and you connect it to the galvanometer. If the rod is constant at one point in magnetic field then nothing happens but if the rod is moving continuously in a magnetic field then an EMF is induced between the end if the rod causing current to flow. This is because when you move the metal rod through the field, you are moving all the electrons in the rod and voltage is produced. This is called a Motional EMF. This emf is used in airplanes. As the plane flies through the Earth's magnetic field, an emf is induced between the wingtips.

Formula OF Motional EMF

The following is the formula of the motional emf:

E = vBL

Methods to Induce EMF

There are the two methods to induce emf which are as follows:

Statically Induced EMF

Statically induced EMF is defined as “The emf induced in a coil due to change of flux linked with it is called Statically Induced EMF.” Transformer is an example of statically induced emf. Here the windings are stationary and the magnetic field is moving around the conductor and produces EMF.

Dynamically Induced EMF

Dynamically induced EMF is defined as “The emf induced in a coil due to relative motion of the conductor and the magnetic field is called dynamically induced emf.” DC generator works on the principle of dynamically induced emf.