Choke:
Choke is nothing but a Transformer. To limit the current in the circuit and to increase the force(Voltage) it is used.
Now observe below figure
There will be two terminals at both the ends of tube in which two terminals are connected to the starter/thermocouple. And two will serve as phase and neutral.
Choke is connected in series with phase as the tube as hallow space immediately after supply is switched on the electrons won't flow through the hallow space, so Choke is used to increase voltage to free electrons in the hallow space. It also serves for below purposes.
1.Fuorescent lamp is supplied with constant voltage, which it causes high current in to the hot electrode. Due to high current electrode may get damage. So to minimize the current Choke is used.
2. By minimizing current voltage increases, So the mercury vapour and organ in the hallow space bombard each other and electrons will move freely from one end to another.