In an important experiment used to determine the nature of atoms, a gas like hydrogen, neon or mercury is excited by sparking it with electricity. the light emitted is separated out into individual colors using a prism or diffraction grating and a few lines of colored light are seen. the light observed in such a spectrum is emitted when an electron in an atom

"jumps" from one energy level down to another lower energy level.

Explanation:

The light observed in such a spectrum is emitted when an electron in an atom "jumps" from one energy level down to another lower energy level. When an electron does this , it emits energy equal to difference in the energy level of two shell in which the electron jumps.

And this emitted light is separated out into individual colors using a prism or diffraction grating and a few lines of colored light are seen.

measure their densities same density, same sub