6  REFRACTION THROUGH A PRISM
Figure 9 21 shows the passage of light through
a triangular prism ABC The angles of incidence
and refraction at the first face AB are i and r1,
while the angle of incidence (from glass to air) at
the second face AC is r2 and the angle of refraction
or emergence e The angle between the emergent
ray RS and the direction of the incident ray PQ
is called the angle of deviation, d