The mercury and sodium street lamps light up because of :

Options

A. Atomic emission
B. Atomic absorption
C. Electron emission
D. Electron Absorption

Answer

A

Explanation

The light in sodium vapour lamp and mercury vapour lamp is, because of electron emission. In case of Sodium of Lamps, Filaments of the sputter fast moving electrons, which hit the sodium atoms (vapour) causing the valence electrons of the sodium atoms excite to higher energy levels and the electrons thus excited relex by emitting the characteristic monchromatic bright yellow light. The mechenism in mercury. The vapour lamp is more involved and sequential. The sputtered elelctrons from the filaments after having been accelerated by high voltage, hit the excited electrons of mercury atoms relex by emitting characterstic but ultraviolet light.