Choke coil – principle, working, and construction, class 12

In this article, we will discuss the Choke coil – principle, working, and construction, so let’s get started…

What is a Choke coil?

What is a Choke coil?
Choke coil

A choke coil is simply an inductor with large inductance that is used to reduce the current in a.c. circuits without much loss of energy.

Principle of a choke coil

The working of a choke is based on the fact that when a.c. flows through an inductor, current lags behind the emf by a phase angle of $\pi / 2 \mathrm \;{rad}$.

Construction of a choke coil

It is made of thick insulated copper wire wound closely in a large number of turns over a soft-iron laminated core. Choke coil offers a large reactance $X_L=2 \pi f L$ to the flow of a.c. and hence current is reduced. A laminated core reduces losses due to eddy currents.

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Working of a choke coil

As shown in the Figure below, a choke is put in series across an electrical appliance of resistance $R$ and is connected to an a.c. source. This forms an $L R$-circuit.

Choke coil - principle, working, and construction, class 12

The average power dissipated per cycle in the circuit is –

$$P_{a v}=V_{eff} I_{eff} \cos \phi=V_{eff} I_{eff} \cdot \frac{R}{\sqrt{R^2+\omega^2 L^2}}$$

Inductance $L$ of the choke coil is very large so that $R<<\omega L$. Then
Power factor, $\cos \phi \simeq \frac{R}{\omega L} \simeq 0$
i.e. the Average power dissipated by the coil is very small. As $Z=\sqrt{R^2+\omega^2 L^2}$ is large, so current is reduced without appreciable wastage of power.

Preference of choke coil over the ohmic resistance

A choke coil reduces the current in a.c. circuit without consuming any power. When an ohmic resistance is used, current reduces but energy losses occur due to heating. So a choke coil is preferred.

Application of choke coil

The most common use of choke coil is in fluorescent tubes with a.c. mains. If the tube is connected directly across $220 \mathrm{~V}$ source, it would draw large currents which would damage the tube.

With the use of a choke coil, the voltage is reduced to an appropriate value, without wasting any power. Choke coils are also used in various electronic circuits, mercury lamps, and in sodium vapor lamps.

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