This phenomenon is called
refraction of light Snell experimentally obtained the following laws
of refraction:
(i)
The incident ray, the refracted ray and the
normal to the interface at the point of
incidence, all lie in the same plane (ii) The ratio of the sine of the angle of incidence
to the sine of angle of refraction is constant Remember that the angles of incidence (i ) and
refraction (r ) are the angles that the incident
and  its refracted ray make with the normal,
respectively