All objects at a given temperature emit thermal radiation, which results in a co

Question

All objects at a given temperature emit thermal radiation, which results in a continuous spectrum. Given that the discharge tubes were at some temperature (~50 C), use Wien's displacement law to argue why you dont see the continuous spectrum when looking at the gas with the spectrometer. When looking at hydrogen with the spectrometer, how many lines do you see? What happens to the spacing between the lines, as the lines get closer to the UV range? Why? Are there transitions of higher or lower energy that we dont see? How many total transitions are there for hydrogen?

Explanation / Answer

Solution1

Genrally all objects which are above the 0k temparature emits the radiation and will give the continuous spectrum.here,in spectrometer discharge tubes were at 50 oC temperature and will give the thermal radiation,but,in spectrometer the radiation obeys the interference condition,that's why we see only constructive interference for the wavelengths which satisfies the equation d*sin(theta)=n*lambda only. so,all wavelengths are emitted but only specific wavelength appear where we observe a constructive interference.hence we don't see a continuous spectrum and we see only discrete spectrum.

Solution2

When the emission of an excited hydrogen atom is viewed through a spectrometer, multiple spectral lines could be observed belonging to the Lyman , Balmer, Paschen, Brackett , Pfund , Humphreys .. and futher series. The exact number of spectral lines that can be seen depends upon the what state the hydrogen atom has been excited to.

In the UV range ( corresponding to Lymna series ) the wavelenghts become very similar i.e the spacing between the lines become smaller and smaller.This happens as the energy differences between the successive excited states keeps descreasing. Thus the transition energy does not increase much, hence close lines.

There are transitions of higher energy like the UV radiation in Lymna series that we cannot see. There are low energy spectral spectral lines in Pfund ( n=6 to n=5) and Hymphreys series (n=7 to n=6 transitions) that is not detected by human eye.

if you consider upto n=6 ( i.e Humphreys series) there could be 6*6 = 36 possible transition routes for hydrogen.

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.