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. On the other hand, there is no dissipation of power when a current flows through a pure inductor.
It consists of a large number of turns of insulated copper wire wound over a soft iron core. A laminated core is used to minimize eddy current loss (Figure).
Fig: Choke coil