Some typical lengths in the universe.

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Some typical lengths in the universe

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How many Balmer series lines are in the visible part of the spectrum?

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  Qu. How many Balmer series lines are in the visible part of the spectrum? Answer: The Balmer series or Balmer Lines are one of the sets of six named series which describe the spectral line emission of the hydrogen atom. The Balmer series is characterized by the electron making the transition from  n ≥ 3   t o   n = 2 . Where n is principal quantum number of the electron. The visible spectrum of light from hydrogen displays 4 wavelengths, 410 nm, 434 nm, 486 nm, and 656 nm. These wavelengths are corresponding to the emission of photons by electrons in excited making the transition to the quantum level having principal quantum number n=2. Therefore, 4 Balmer series lines are in the visible part of the spectrum.
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Tropical Year

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The definition of the tropical year   The tropical year is defined as the time interval between two successive passages of the earth through the vernal equinox, which takes place approximately on March 21st  each year. It may also be defined as 1/86,400 of the mean solar day, which is the time interval between two successive passages of a point on the earth in front of the sun average over one year. But this definition has the drawback that, because of tidal action the period of earth's rotation is decreasing gradually, and therefore this unit should also be changing gradually.
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