Question

Give the working principle of choke coil. Explain the importance of alternate current in choke coil.

Answer 1

Hint: A choke coil works by the principle of self induction. Its main function is to provide AC resistance to the circuit. At the same time, it does not allow any resistance to the DC current. Lentz’s law plays an important role in the working principle of the choke coil.
Formula used:
$\epsilon=L\dfrac{di}{dt}$

Complete step-by-step solution:
A choke coil is basically a coil with very high self-inductance and very low resistance.

Self-inductance is defined as the magnetic flux linked with the circuit due to unit current through it. Alternatively, it can also be defined as the electromotive force that is generated due to unit change of current in unit time.
Now we know, in AC circuit the current changes with time very fast. So, if the self-inductance of the coil is very high, the electromotive force (emf) generated in the coil will also be very high. This emf $\epsilon$ always works against the source voltage to satisfy the Lentz’s law.
Lentz’s law states that the generated emf will always try to stop the cause of its own generation. So, here the emf tries to stop the changing AC current. The value of the emf is,
$\epsilon=L\dfrac{di}{dt}$
Here, L is called self- inductance, i is the current.
This gives an impedance to the AC current.
But due to very low resistance, the power dissipation through a choke is very low. So, this makes a choke economically efficient.
Additional information:
The unit of inductance is Henry. ‘L’ gives a measure of the emf generated in the coil due to its own changing current. There is another thing called mutual inductance. It is the emf in one coil due to change of current in another coil.

Note:
- The opposite concept of a choke is a non-inductive coil. It gives no AC impedance to the circuit, but has a very high resistance.
- A choke is mainly used to provide the required resistance in an AC circuit without causing DC power loss.
- The magnetic flux due to a coil's own current is given as $\phi=L.i$ .