SNC 2D
Images in Plane Mirrors
A plane mirror is a mirror with a flat, reflective surface. Scientists call an
object placed in front of a mirror the object, and they call the likeness that
is seen in the mirror the image of the object.
If you apply the laws of reflection to rays going from the object to the
mirror, you can predict where the image will be and what the image will
look like.
Since light rays travel in a straight line, to find where the eye “sees” the
image in the mirror, extend the rays on a ray diagram backwards (using
dashed lines) until they meet at a point behind the mirror. The point at
which the dashed lines meet is the location of one point on the object. If
you repeat this for several points, you can find out exactly where the image
of the object is located.
(see Table 10.1 on pg. 416)
Virtual vs. Real Images
There are no light rays actually going to or coming from the image behind
the mirror – they only appear to be coming from the image. This is called a
virtual image.
One way to decide if an image is real or virtual is to imagine putting a screen
at the location of the image – if light rays hit the screen and form an image,
then the image is real; if not, it is virtual.
Since there is no way for light rays to get behind a plane mirror, the image is
virtual. Curved mirrors, however, are capable of creating a real image
(more on that later in the unit!).
Characteristics of Images
In general, an image has four characteristics (use the acronym SALT):
Size – is the image the same size, larger than, or smaller than the object
Attitude – i.e., orientation – is the image upright or inverted (upside down)
Location – closer to, farther than, or the same distance as the object
Type – real image or virtual image
In a plane mirror:
 The image is the same size as the object
 The image has the same attitude as the object (i.e., upright)
 The image is the same distance from the mirror as the object
 The image is virtual