http://www.ck12.org Chapter 21. Physical Optics
Equation 2:n=cv
Substitutefλfrom Equation 1 forvin Equation 2.
nair=fcλandn=fcλn,
Now recall that the frequency remains unchanged as the wave travels from one medium to another.
From the rationairn:
nair
n =fcλ
fcλ
n
=λλn→,but nair= 1 →^1 n=λλn→λn=λn.
In simpler language, we can say:λ=vf, and sincefis constant, whenvis reduced by a factorn, so isλ.