When the refractive indices are different, the light is refracted causing light to converge on one half of the specimen, thereby creating a shadow effect on the opposite side.
(the refractive indices; are; different) (the light; is refracted; causing light to converge on one half of the specimen; T:When the refractive indices are different)
the refractive indices the light
are is refracted
different
causing light to converge on one half of the specimen T:When the refractive indices are different