**Working Procedure of Choke Coil:**

A choke coil is an inductance coil of very small resistance used for controlling current in an a.c. circuit. If a resistance is used to control current, there is wastage of power due to Joule heating effect in the resistance.

The inductive reactance offered by the coil is given by X_{L} = ωL

In the case of an ideal inductor the current lags behind the emf by a phase angle π/2.

∴ The average power consumed by the choke coil over a complete cycle is

**P _{av} = E_{rms} I_{rms} cos π/2 = 0**

However in practice, a choke coil of inductance L possesses a small resistance r. Hence it may be treated as a series combination of an inductor and small resistance r. In that case the average power consumed by the choke coil over a complete cycle is

P_{av} = E_{rms} I_{rms} cos φ

**P _{av} = E_{rms} I_{rms }[r/( r ^{2} +ω^{2} L^{2})] … … (1)**

where, [r/( r ^{2} +ω^{2} L^{2})] is the power factor. From equation (1) the value of average power dissipated works out to be much smaller than the power loss I2R in a resistance R.

Fig: a A.F Choke Fig: b R.F. Choke

Chokes used in low frequency a.c. circuit have an iron core so that the inductance may be high. These chokes are known as audio – frequency (A.F) chokes. For radio frequencies, air chokes are used since a low inductance is sufficient. These are called radio frequency (R. F) or high frequency (H.F) chokes and are used in wireless receiver circuits (Fig: a and Fig: b).

Choke coils can be commonly seen in fluorescent tubes which work on alternating currents.

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