why do we have different formulaes of angular momentum for every quantum no. ?

Hi

Its because angular quantum number (l) value is different for different principal quantum number.

n = 1, L = 0, Lyman series (ultraviolet)
n = 2, L = √2ħ, Balmer series (visible)
n = 3, L = √6ħ, Ritz-Paschen series (near infrared)
n = 4, L = 2√3ħ, Brackett series (short-wavelength infrared)
n = 5, L = 2√5ħ Pfund series (mid-wavelength infrared).