posted by SABRINA .
a circular opaque disk, 25 cm in diameter, is set up 30 cm from a circular source of light of diameter 40 cm. Ascreen is placed 30 cm beyond the opaque disk. Describe, giving dimensions, the nature of the shadow on the screen.
Ok, I have drawn a sketch and can say that the shadow formed is the umbra which is in the middle surrounded by 2 other sections called penumbra.
how do i calculate the shadow?