Michael Faraday was born on 22nd September 1791 in a very poor family in London. He joined as a News paper boy at his 13th year. He was later appointed to the Royal Institute of London. In 1821 he published his work on electromagnetic induction. In 1825 he became the Director of Royal Institute. He introduced new scientific technology like anode, cathode, anion, cation, electrode etc.,
When he was employed as an errand boy for a book binder, a customer gave him tickets for some scientific lectures which sir Humphrey Davy was giving at Royal institution. Here he attracted the interest of sir Humphrey, and finally was appointed as his lecture assistant, thus escaping from the commerce he formed distasteful to the science he loved.
KEY WORDS
* Magnetic flux * Magnetic flux density
* Electric motor * Slip rings
* Induced current * Induced E.M.F.
* Electric generator * DC and AC currents
* Faraday's Law * Solenoid
* rms values * Lenz's Law
* Right hand thumb rule
KEY WORDS - EXPLANATION
Magnetic flux: The number of magnetic field lines passing through the plane area. 'A' perpendicular to the field is called magnetic flux. It is denoted by Φ.
Magnetic flux density (B): Magnetic field density is defined as the magnetic flux passing through unit area taken perpendicular to the field B. It is also known as magnetic field induction.
Electric motor: In electric motor, electrical energy is converted into mechanical energy.
Slip rings: Two small hallow cylinders made up of Copper attached to the two ends of the coil which make sliding contact with Carbon brushes.
Induced current: Whenever there is a continuous change of magnetic flux linked with a closed coil, a current is generated in the coil. The current generated is called induced current.
Induced E.M.F.: The E.M.F. generated in the coil whenever there is a continuous change of magnetic flux linked with the closed coil.
Electric generator: A machine which converts mechanical energy into electrical energy.
A.C.: An electric current that reverses its direction and magnitude with a constant frequency.
D.C.: An electric current in which the net flow of charge is in one direction only.
Faraday's Law: Whenever there is a continuous change of magnetic flux linked with a closed coil, a current is generated in the coil.
Solenoid: A solenoid is a long wire wound in a close packed helix.
Where I0 and V0 are the peak values of A.C. and A.C. E.M.F. rms value of an alternative current/ voltage is taken as that value of direct current which will produce the same amount of heat in a given resistor for a given time.
Lenz's Law: The induced current will appear in such a direction that it opposes the changes in the flux in the coil.
Right hand thumb rule: If we grab the current carrying wire without right hand in such a way that the thumb is in the direction of current, then the curled fingers show the direction of the magnetic field.
SYNOPSIS
* A magnetic field exists in the region surrounding a bar magnet and is characterised by the strength and direction.
* The direction of the magnetic field can be determined by using a compass.
* Magnetic lines of force are imaginary lines. These lines help us to understand the nature of the field.
* From the magnetic lines of force around a bar magnet we can conclude that the field is strong when lines are crowded and the field is weak when the lines are spaced apart.
* The number of magnetic lines passing through the plane of area 'A' perpendicular to the field is called magnetic flux and is denoted by Φ.
* The S.I. unit of magnetic flux is Weber.
* Magnetic flux density (B) is defined as the magnetic flux passing through unit area taken perpendicular to the field. This is also known as magnetic field induction.
* Units of magnetic flux density is Weber/ (meter)2. This is also called Tesla.
* A current carrying conductor produced a magnetic field around it and the direction of the magnetic lines of force can easily be determined with right hand thumb rule.
* If we grab the current carrying wire with our right hand in such a way that thumb is in the direction of current, then the curled fingers show the direction of magnetic field.
* The direction of the magnetic field due to a coil or solenoid is determined by using right hand rule.
* When we curl our right hand fingers in the direction of the current, thumb gives the direction of the magnetic field.
* A solenoid is a long wire wound in a close packed helix.
* The magnetic field lines setup by a solenoid resemble those of a bar magnet indicating that a solenoid behaves like a bar magnet.
* One end of the solenoid behaves like a north pole and the other behaves like a south pole.
* The field lines outside the solenoid are continuous with those inside, outside the solenoid the direction of field lines is from north to south while inside the direction is from south to north.
* Current carrying wires produce magnetic filed. So electric charges in motion produce magnetic fields.
* The magnetic force 'F' acting on a charge q is F = qvB. This holds good when the direction of charged particle 'V' is perpendicular to the direction of magnetic field 'B'.
* It is experimentally proved that when there is an angle between direction of field and velocity the magnetic force experienced by the charge is given by F = qvB sin θ.
* When charges move parallel to the magnetic field the value of θ = 0. So sin θ = 0. Thus the charge experiences no force when it is moving parallel to the magnetic field.
* It is easy to find out the direction of magnetic force acting on a charge moving in a magnetic field.
* We have to put our right hand fingers along the direction of velocity of moving charge and next curl our fingers towards the direction of magnetic field then our thumb gives the direction of magnetic force.
* Generally right hand rule is used when velocity and field are perpendicular to each other.
* Right hand rule states ''If the fore - finger points towards the direction of velocity of charge or current, middle finger points to the direction of field (B), then thumb gives the direction of force when the three fingers are stretched in such a way that they are perpendicular to each other".
* This rule is applicable to positive charge.
* To find the direction of force acting on negative charge, we have to first find the direction of force acting on positive charge. Next we have to reverse its direction. This new direction is the direction of force acting on the negative charge.
* The force acting on the current carrying wire kept in a uniform magnetic field at an angle θ is F = ILB sin θ.
Where L is the length of the conductor.
* Right hand rule helps us to find the direction of magnetic force exerted by the magnetic field on current carrying wire. It does not help us to explain the reason for deflection of wire.
* To understand the working of an electric motor we need to understand the behaviour of a current carrying coil kept in a uniform magnetic field.
* In electric motors, the electrical energy is converted in to mechanical energy.
* "Whenever there is a continuous change of magnetic flux linked with a closed coil, a current is generated in the coil". This is one form of Faraday's Law.
* The induced E.M.F. generated in a closed loop is equal to rate of change of magnetic flux passing through it.
* Induced E.M.F. 
* The induced current in the coil will appear in such a direction that it opposes the changes in the flux in the coil.
* Electromagnetic induction is all around us.
* During security check, people are made to walk through a large upright coil of wire which produces a weak AC (alternating) magnetic field. If we are carrying any significant quantities of iron, the magnetic flux linked with the large coil changes and the induced current generated in the coil triggers an alarm.
* An induction stove works on the principle of electromagnetic induction.
* In alternating current (AC) the direction of charge flow reverses periodically. So AC possesses certain frequency.
* AC - E.M.F. and AC are expressed in terms of rms values.
* Let I0 and V0 be the peak values of AC and AC - E.M.F.
* In generators, mechanical energy is converted into electrical energy.
Writer: C.V. Sarveswara Sarma
