in step index fiber the core of diameter D has a refractive n1, which is typically equal to 1.48. core is typically surrounded by the cladding of slightly lower index. Where n2=n1(1-delta). The parameter is simply called the index difference. Based on this consider a multimode fiber that has a core refractive index of 1.48 and core cladding index difference of 2%. Find numerical aperature, the acceptance angle and the critical angle.