5. The adjacent figure shows cross section of a hollow glass tube of internal radius r, external radius R and index of refraction n. For two rays DE and ABC (in which DE lies on ODE and DE is parallel to BC), the separation r1 will be
correct answer is c
apply snell's law at the outer surface, u will get sin B= nr/R(B is the angle of refraction on going out from the tube)
then r1=RsinB=nr