For refraction at a stationary spherical surface, which statements are correct?

Select all that apply

• Option A

  μ₂/v-μ₁/u=(μ₂-μ₁)/R.

• Option B

  A radial ray is normally incident.

• Option C

  If μ₁=μ₂, refracting power is zero.

• Option D

  The two focal lengths always have equal magnitudes.