The picture is an emission spectrum of Helium. The spectrum has sharp lines (peaks) at certain wave lengths characterizing it as helium. Agreed that it characterizes Helium as atomic spectral line characterize gases and they are based on allowed energy states of electrons in an atom.
Well and good, but what i don't know is the $y-axis$. what does it represent? It is shown as intensity (counts) but I want to know what it is and how does it vary from element to element. Does this count also characterize the elements, or is it same for all elements? Appreciate if you could throw some light on it.
Question : I mean if i keep the position of lines(pulses) same but change their relative amplitudes, what happens? does it represent a different gas?
Picture taken from the internet.
Best Answer
Here is the spectrum taken as a photo:
Note the difference in the visible intensity of the lines registered. In your spectrum instead of a film there is a counter which measures the number of hits at that wavelength from the excited helium.
The location of the excitations on the wavelength axis identifies the atom uniquely, like a fingerprint a person to the police. The intensity/counts is secondary to the identification, though it is characteristic it can depend on the intervening medium ( glass, air, space dust for astronomical observations).