Question

The induction coil works on the principle of.
a) Self induction
b) Mutual induction
c) Ampere's law
d) Fleming's right hand rule

Answer 1

Induction in general is a process of inducing a change into something due to something else. Inductions coils when placed in a changing magnetic field, induce a change in a physical quantity. This change is caused by the coil itself hence we can manipulate accordingly the incorrect options and approach to our answer.

Complete answer: To begin with let us understand how an induction coil works and hence accordingly the principle behind it would be revealed.

In the first diagram the key is closed in the circuit. To understand induction, the value of current in the circuit initially when the key is just plugged in, its value does not reach directly to its maximum. It takes some time, let us say t. In this time the value of current in the circuit keeps on changing.
An inductor coil can basically be considered as a solenoid . Hence, magnetic field B produced when the current is passed through the inductor is given by $B={{\mu }_{\centerdot }}ni$ where i the current through the inductor, n is the number of turns per unit length and ${{\mu }_{\centerdot }}$ is the permeability of free space.
By law of electromagnetic induction we can say that,

Change in flux across a coil i.e. $\text{Emf =}\dfrac{d\phi }{dt}=\dfrac{dBA\operatorname{Cos}\theta }{dt}$ where B is the magnetic field across the coil A is the area of cross section and $\theta$ is the angle between the coil and B. in the above case that is our inductor $B={{\mu }_{\centerdot }}ni$ and $\theta ={{0}^{\centerdot }}$, hence the emf induced is given by $A{{\mu }_{\centerdot }}n\dfrac{di}{dt}$. From this equation we can conclude that as current changes emf will be induced in the circuit. As the coil induces emf due to the magnetic field of its own the above process is called self induction.
So, the correct answer is “Option A”.

Note:
It is to be noted that the emf induced is different when the switch is just turned on and when the switch is turned off. The direction of the current induced is given by Lenz law which states that the polarity of the induced emf is such that it opposes the change in magnetic flux that produced it.