Question

Why is choke coil needed in the use of fluorescent tubes with ac mains?

Answer 1

Hint: A fluorescent tube produces light by the phenomenon of fluorescence. It has mercury vapor inside it which gets excited and emits UV rays which cause phosphor on the walls of the tube to glow and produce light.

Complete step-by-step answer:
Inside a fluorescent tube, there is mercury vapor which gets excited when a very high potential difference or voltage is applied across it. The vapor gets excited and produces ultraviolet radiation which interacts with the phosphor coating on the inner walls of the tube light and the phosphor produces the glow of the light emanating from the tube light.
A choke coil is used to produce this high voltage across the tube. A choke coil is essentially an inductor. An inductor is used because unlike a resistor, a choke coil does not dissipate energy in the form of heat when current passes through it. A choke coil has inductive reactance which does not cause energy dissipation. It is also much easier to control AC mains using inductors such as the choke coil.
This makes a fluorescent tube much more efficient in terms of power used and light produced than normal incandescent bulbs. This is because incandescent bulbs dissipate a lot of energy in the form of heat when current passes through the filament.

Note: Fluorescent tubes are already being phased out for the other better alternatives which are LED bulbs. LEDs or ‘Light Emitting Diodes’ are simple p-n junction diodes which produce light when an excited electron falls back from the conduction band to the valence band. The band gap of LEDs can be altered by using different materials and thus, the energy (and hence, wavelength and color) of the light being emitted can be altered.