Light from an object is reflected
by a plane mirror. The shaded side of the object is
marked with a symbol. The mirror produces an image of the
object, as shown in the following figure. Which of the following figures
correctly shows the object if it is rotated so that the shaded side of it faces away
from the mirror? The base of the object remains in
contact with the surface that it initially rests on while the object is rotated. Is it option (A) or option (B)?
This question is asking if images
seen in a mirror are reversed. It is sometimes said that an image
in a mirror is the reverse of an object that is in front of the mirror.
To see if this is correct, let’s
consider some light rays from an object in front of a plane mirror that reflect from
the mirror. In this sketch, the object and
image are both aligned parallel to the mirror. Notice that the top of the object
and the top of the image can be connected by a line that is at 90 degrees to the
mirror. The same thing is true for the
bottoms of the object and image.
Let’s say that now we rotate the
object around its center so the top and bottom are reversed. If we were observing the object
from behind, we would see a color reversal as the object goes through its
rotation. In the same way, when the object in
the original diagram is rotated, the symbol on it will be reversed. Therefore, the symbol will not look
like the symbol in option (B), which has not been reversed, but rather it will look
like the symbol in option (A), which is reversed.
For our answer then we choose
option (A). This is how the object would appear
if it is rotated so its shaded side faces away from the mirror.