The Emission Spectra of Gaseous Discharge Tubes

What type of spectrum is emitted by gaseous discharge tubes?

Options: 1. Continuous spectrum 2. Line spectrum 3. Absorption spectrum 4. Emission spectrum

Final answer:

Gaseous discharge tubes emit a line spectrum or an emission spectrum, which occurs when electrons in the gas are excited and then emit light at specific wavelengths as they return to lower energy levels, producing discrete emission lines unique to each element.

Explanation: The type of spectrum emitted by gaseous discharge tubes is known as a line spectrum or an emission spectrum. When electricity is applied to the gas contained at low pressure within the tube, it causes electrons to become excited to higher energy levels. As the electrons return to lower energy levels, they emit photons of light. This light, which appears as a distinctive color unique to each type of gas, can be passed through a prism or diffraction grating to separate it into its constituent wavelengths. Because each element has a unique electronic structure, the emitted photons correspond to specific energy differences, resulting in a series of discrete emission lines rather than a continuous spectrum.

For instance, a tube filled with hydrogen gas will emit a blue-pink color, and passing this light through a prism reveals an emission spectrum consisting of photons of four visible wavelengths. Similarly, neon signs operate as gas discharge tubes, producing their characteristic glow.