Question

a). Over what (approximate) wavelength range is the emission of light from excited sodium atoms most sensitive to the eye? HINT: sodium vapor lamps are used for public lighting of streets, parking areas, ect.

b).Over what (approximate) wavelength range is the emission of light from excited mercury atoms most sensitive to the eye? HINT: mercury vapor lamps are also used for public lighting of streets, parking areas, ect.

Answer 1

1. The visible light corresponds to a wavelength range of 400 - 700 nm and a color range of violet through red.Sodium atoms in an excited state produce light at a characteristic wavelength near 589 nm (two dominant spectral lines are present very close to each together at 589.0 and 589.6 nm).In sodium-vapor bulb, the sodium gas tends to emit more photons in the longer wavelength region (leading to yellow/orange color) of the spectrum.Thus yellow/orange color falling in the wavelength range of 589 nm is most sensitive to our eye.

2. Clear mercury lamps lead to the production of white light with a bluish-green tint due to the combination of spectral lines of mercury.Mercury-vapor bulbs tend to cover entire visible region (200-600 nm).More number of photons are emitted in the region of shorter wavelength region of the spectrum leading to a bluish light falling in the wavelength range of 450-495 nm, is perceived by our eye.