Electricity and magnetism are both related to each other. Electricity can be generated with the help of a magnetic field and vice versa a magnetic field can be created using electricity. A number of electrical and electronic gadgets work on the principle of electromagnetism.
Faraday and Lenz discovered the relationship between electricity and magnetism. When a magnetic field is changing at a particular rate near a conductor, it forces the free electrons inside the conductor to move back and forth. The working of transformer and electric generator is based on this principle.
First Law: When electric current flows through a conductor, a proportional magnetic field is produced around the conductor.
The important factors of the first law are as follows –
The magnetic field around the conductor is in the form of magnetic lines of force called magnetic flux (f).
Its strength is closer to the conductor and decreases as we go away from the conductor.
The strength of the magnetic field produced around the conductor is directly proportional to the magnitude of current flowing through the conductor.
If the conductor is straight, the magnetic field will have a shape of concentric circles around it. However, if its shape is like a coil (or any other complex shape) then the geometrical orientation of the magnetic field will also be complex.
Second Law: When a conductor is placed in a changing magnetic field, proportional induced e.m.f. and current are produced in the conductor.
The important factors of the second law are as follows –
This induction occurs because the free electrons move back and forth within the conductor due to changing magnetic field to produce electric current.
The magnitude of e.m.f. produced within the conductor is directly proportional to the rate of change of magnetic flux.
If the shape of the conductor is like a coil, then its number of turns decides the magnitude of induced e.m.f. within the conductor.
The number of magnetic lines of force (or magnetic flux) decides the magnitude of induced current.
Basic idea: When current flowing through a conductor changes, a counter e.m.f. is induced across the conductor. This induced voltage has the tendency to oppose any change in current flowing through the conductor. This means that the induced voltage has opposite polarity with respect to the initial voltage applied across the conductor.
The above phenomenon is possible only for AC current. This is because when AC current flows through a conductor, magnetic flux varies its strength and direction. This is similar to the motion of magnetic flux. However, when DC current flows, voltage induction is not possible as DC current is steady and its flow is unidirectional. Thus, Lenz’s law is a direct consequence of law of conservation of energy.
Consider a coil connected across a battery through a variable resistor to flow some current through it. When we try to increase this current (and hence flux) through the conductor, it is always opposed by immediately producing counter e.m.f. In the same way, if we try to decrease the current, again it is delayed due to the production of self-induced e.m.f. Every time we do this, the energy required to overcome this opposition is supplied by the battery. This energy is stored in the additional flux produced. Thus, it can be treated as a similar example to the inertia of a material body.
The converse is also true. The second coil can induce an e.m.f. in the first coil when current in the second coil changes. This ability of reciprocal induction is measured in terms of coefficient of mutual induction (M). This phenomenon of mutual induction is basically used in a transformer.
Sir, V. (n.d.). Faraday’s Laws & Lenz’s Law: Basic Comparison | Vidyasagar Sir's Electronics Web. Vidyasagar Sir's Electronics Web. Retrieved March 8, 2013, from http://vsagar.com/2011/11/11/shortcomings-in-faradays-laws/