Electromagnetic induction

Electromagnetic induction is a process in which a conductor cuts through a stationary magnetic field lines (or conductor placed in a changing magnetic field) causes the production of a voltage across the conductor. The voltage produce is called induce EMF and causes current called induce current.

The large generators in power stations generate the electricity we need using this process.

Current is created in a wire when:

• the wire is moved through a magnetic field (‘cutting’ the field lines)
• the magnetic field is moved past the wire (again ‘cutting’ the field lines)
• the magnetic field around the wire changes strength.

Current created in this way is said to be induced.

The faster these changes, the larger the current.

In practice, the changes are induced in a coil of wire because the current created is increased by the number of turns of wire in the coil. The wire used must not be too thin as carrying the current will then cause it to overheat. Note that the induced current will flow in a direction that opposes the movement of the wire.

Lenz’s Law:

This law is named after the German physicist Heinrich Friedrich Lenz (1804–1865), who announced it in 1833. Lenz’s law enables us to determine the direction of the induced current in the coil. It states that:

The direction of an electromagnetically-induced current will be such as to oppose the motion producing it.

Points to Remember

• The movement of conductor (or magnet) should be perpendicular to the magnetic lines.
• Changing magnetic field across conductor is called magnetic flux linkage.
• The law of electromagnetic induction was first presented by Michael Faraday in 1831 and therefore it is also called Faraday’s law of electromagnetic induction.
• This phenomenon is used in design of electric generators and transformers.
• The size of induce emf or induce current produce is proportional to:
1. The relative speed of the motion of conductor and magnet;
2. The number of turns in the coil;
3. The strength of the magnet.

Fleming’s right- hand Rule

Fleming’s right hand rule helps us to predict the direction of induce current relative to the motion of conductor. According to this rule, extend the thumb, forefinger, and the middle finger of the right hand in such a way that all three are mutually perpendicular to each another. If the forefinger points in the direction of the magnetic field from north to south and thumb points in the direction of motion of conductor then middle/central finger points in the direction of the induce current. The induce current is always from negative to positive direction, that is opposite to the direction of conventional current.