Question

why fluorescent tube glows when electricity is passed through it

Answer 1

A Fluorescent tube or Fluorescent lamp is a low pressure mercury - vapor gas - discharge lamp that uses fluorescence to produce visible light. An electric current in the gas excites mercury vapor which produces short - wave ultraviolet light that then causes a phosphor coating on the inside of the bulb to glow. A fluorescent lamp converts electrical energy into useful light much more efficiently than incandescent lamps. The typical luminous efficiency of fluorescent lighting system is 50-100 lumens per watt, several times the efficiency of incandescent bulbs with comparable light output.

Answer 2

Xenon

Gas glows after passing electricity through it