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The mercury and sodium street lamps light up because of :

Answer» <html><body><p> <a href="https://interviewquestions.tuteehub.com/tag/atomic-2477" style="font-weight:bold;" target="_blank" title="Click to know more about ATOMIC">ATOMIC</a> emission</p><br/><br/><p>The light in sodium vapour lamp and mercury vapour lamp is, because of electron emission. In case of Sodium Lamps, filaments of the lamp sputter <a href="https://interviewquestions.tuteehub.com/tag/fast-456451" style="font-weight:bold;" target="_blank" title="Click to know more about FAST">FAST</a> moving electrons, which hit the sodium atoms (vapour) causing the valence electrons of the sodium atoms to excite to higher energy levels and the electrons thus excited relax by emitting the characteristic monochromatic bright <a href="https://interviewquestions.tuteehub.com/tag/yellow-1464953" style="font-weight:bold;" target="_blank" title="Click to know more about YELLOW">YELLOW</a> light. The mechanism in mercury vapour lamp is more <a href="https://interviewquestions.tuteehub.com/tag/involved-7257329" style="font-weight:bold;" target="_blank" title="Click to know more about INVOLVED">INVOLVED</a> and sequential. The sputtered electrons from the filaments, after having been <a href="https://interviewquestions.tuteehub.com/tag/accelerated-366473" style="font-weight:bold;" target="_blank" title="Click to know more about ACCELERATED">ACCELERATED</a> by high voltage, hit the mercury atoms. Here also, the excited electrons of mercury atoms relax by emitting characteristic but ultraviolet light.</p></body></html>


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