Inductance | What is inductance? | What is an inductor?



Inductance | What is inductance? | What is an inductor?
According to Faraday’s law of electromagnetic induction, “Whenever there is a change in current flowing through a coil, a change in magnetic field is produced which induces a voltage across the coil.” A coil is nothing but a twisted wire. When such a coil is formed out of a wire of certain length and cross-sectional area, it acts as an inductor. The electromagnetic field produced by the inductor depends on the current flowing through it. The field so formed expands with an increase in current and contracts with decrease in current.

 

What is an Inductor?

As mentioned above an inductor is a twisted wire of specified length and radius. Inductors do not dissipate energy but stores it in the form of magnetic field. Inductance is normally denoted by the alphabet L
L = (N2µA)/l
Where,
N is the number of turns of wire,
µ is the relative permeability of the material over which the coil is wound,
A is the cross sectional area of the coil,
L is the length of the coil.

Unit of Inductance

Unit of inductrance is henry. It is denoted by the letter H. One henry is equal to the inductance developed in a coil when current through it changes at a rate of one ampere per second.

Symbol of inductance


Inductance | What is inductance? | What is an inductor?


Current voltage relationship in inductance

Inductance | What is inductance? | What is an inductor?

 

V = L x di/dt  --------------------------------- Equation -1

where,
V is the voltage across the inductor in volts and i is the current flowing through it.


The above equation can be rewritten as follows:


Inductance | What is inductance? | What is an inductor? --------------------------------- Equation -2

The above equation denotes that the current through an inductor depends on initial current and the voltage across its terminals.

Power absorbed by an inductor

Power absorbed by an inductor, P= vi= V = Li x di/dt

Energy stored in an inductor

Energy stored in an inductor, E = ∫p.dt = ∫ Li x di/dt = Li2/2

Key points about inductor that has to be noted

  1. Refer equation 1, the voltage across an inductor depends on the change in current through it. Hence when the current is constant, the voltage across its terminals would fall to zero. This means that for a DC supply (constant current supply), inductor acts as short circuit.
  2. An inductor can store finite amount of energy even if the voltage across its terminal is zero.
  3. As mentioned before, an inductor should never dissipate energy. But practically, a small amount of energy dissipation occurs across an inductor due to the resistance of the coil.

Problems based on inductance

Find the voltage induced across an inductor having an inductance of 2H, if the current through it varies at a rate of 3 amperes per second for 2 seconds. Also find the energy stored in it.

Solution:
V = L x di/dt
di/dt = 2s x 3A = 6
therefore voltage induce across the inductor V = Lx 6 = 2x6 = 12 V
The energy stored in the inductor = Li2/2= 2 x 62 /2 = 36 joules.


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