Step-by-step explanation:
Light is emitted in a fluorescent tube filled with mercury vapor through a process called fluorescence. Here's a simplified explanation of the key steps:
1. Excitation: When an electric current passes through the tube, it ionizes the mercury vapor, causing some of the electrons in the mercury atoms to become excited. These excited electrons move to higher energy levels within the atoms.
2. De-excitation: Excited electrons are unstable, so they quickly return to their original, lower energy levels. As they do so, they release the excess energy in the form of ultraviolet (UV) photons.
3. Phosphor Coating: The inner surface of the fluorescent tube is coated with a phosphor material. This phosphor coating absorbs the UV photons and re-emits the energy as visible light. The specific wavelengths of light emitted depend on the composition of the phosphor coating.
4. Visible Light Emission: The visible light emitted by the phosphor coating is what we see as the illumination from the fluorescent tube. The phosphor coating is designed to produce a broad spectrum of visible light, which gives off the characteristic white light of fluorescent lamps.
So, in summary, the process involves electrical excitation of mercury vapor, which in turn causes the phosphor coating to emit visible light through the conversion of UV photons to visible wavelengths.