Answer
(a) We could still see the image of the pencil in the mirror.
(b) We could not see the image of the pencil in the mirror.
Work Step by Step
(a) Light rays from the top part of the pencil would reflect off the mirror at about the midpoint and enter the eye. Light rays from the bottom part of the pencil would reflect off the mirror below the midpoint and enter the eye.
Therefore, even if the top half of the mirror is covered, we could still see the image of the pencil in the mirror.
(b) Light rays from the top part of the pencil would reflect off the mirror at about the midpoint and enter the eye. Light rays from the bottom part of the pencil would reflect off the mirror below the midpoint and enter the eye.
Therefore, if the bottom half of the mirror is covered, we could not see the image of the pencil in the mirror.
