Question

3) A hydrogen atom contains just one electron, so it can produce only one wavelength of light (and therefore only one color of light) at a time. Why then do we see many different colors of light simultaneously when we observe the emission spectrum of hydrogen?

Answer 1

When you take the H spectrum

i) we dont use one single atom , but a sample of hydrogen gas which contains a large number of hydrogen atoms.

ii) all these H atoms do not absorb same energy given to t hem. Some absorb more energy and get excited to higher energy levels. some absorb less energy so get into lower excited energy levels.

iii) thus the sample now contains various H atoms at various excited levels.

iV0 when the excited electrons drop down to ground state, they need to release the extra energy in the form of radiation, that is observed as a line in the spectrum.

Thus all the lines we see in the H -emission spectrum correspond to one electronci transition.

v) if more atoms undergo same electronci transition, that particular corresponding line will be more intense.

Since the energy difference betwen first and second orbits is largest all the transitions to first level are observed in UV region and the next higher difference in energy being between 2nd and 3rd, this tranistion releases in the visible region.

Thus more number of atoms in the sample are responsible for so many lines in H-spectrum,