Question

A student uses spactles of focal length -2.5m​

Answer 1

Answer:

Your answer is above ☝☝☝☝☝☝☝☝☝

Answer 2

Answer:

The critical angle is the angle of incidence where the angle of refraction is 90∘

The light must travel from an optically more dense medium to an optically less dense medium.

The critical angle s related to the refractive index as

θc=sin−1(n2/n1)

rearranging

n2/n1 = sin(θc)

given θc= 30∘

by substituting the values

n2/n1 =sin(30∘) = o.5