Question

relation between wavelength and refractive index??

Answer 1

Un = refractive index 
An=wavelength in the medium n
U1 * A1 = U2 * A2 

Answer 2

we know,

refactive index = velocity of light in vaccum /velocity of light in medium

also, velocity of light = wavelength of light × frequency of light

but we know , frequency is not change when light goes from one medium to another medium .

hence, velocity of light Change then, wavelength also change ,

e.g wavelength in medium = wavelength in vaccum or air/ refractive index