kinetic energy of an electron emitted when radiation of frequency ν = . × s – hits the metal. According to Einstein’s equation Kinetic energy = ½ m e v = h ( ν – ν ) = ( . × – J s) ( .
. Evidence for the quantized* Electronic Energy Levels: Atomic spectra The speed of light depends upon the nature of the medium through which it passes. As a result, the beam of light is deviated or refracted from its original path as it passes from one medium to another. It is observed that when a ray of white light is passed through a prism, the wave with shorter wavelength bends more than the one with a longer wavelength.
Since ordinary white light consists of waves with all the wavelengths in the visible range, a ray of white light is spread out into a series of coloured bands called spectrum . The light of red colour which has longest wavelength is deviated the least while the violet light, which has shortest wavelength is deviated the most. The spectrum of white light, that we can see, ranges from violet at . × Hz to red at × Hz.
Such a spectrum is called continuous spectrum. Continuous because violet merges into blue, blue into green and so on. A similar spectrum is produced when a rainbow forms in the sky. Remember that visible light is just a small portion of the electromagnetic radiation (Fig.
. ). When electromagnetic radiation interacts with matter, atoms and molecules may absorb energy and reach to a higher energy state. With higher energy, these are in an unstable state.
For returning to their normal (more stable, lower energy states) energy state, the