Question

The discharge tube uses an electric current with a large voltage. Explain what is occurring at the atomic level that causes the sodium atoms to emit electromagnetic radiation.

Answer 1

The photoelectric effect provides evidence for the existence of the photon and thus the behavior of electromagnetic radiation. The concept of the photon, however, emerges from experimentation with thermal radiation,electromagnetic radiation emitted as the result of a source’s temperature, which produces a continuous spectrum of energies.

Although objects at high temperature emit a continuous spectrum of electromagnetic radiation, a different kind of spectrum is observed when pure samples of individual elements are heated.

When a high-voltage electrical discharge is passed through a sample of sodium at low pressure, the resulting individual isolated sodium atoms caused by the dissociation of $Na$ emit a yellow light. This is because the most intense lines in its spectrum are in the yellow portion of the spectrum, at about $589nm$