Image Characterisitics
Type: Virtual or Real
Orientation: Upright or Inverted
Size: Same, Larger or Smaller
Position: Behind the mirror or
In front of the mirror
Distance from mirror
(same, closer or farther than
object)
1
Images
formed by plane mirrors
6 steps
See handout last class, refer to p. 58
Make sure
-the extended rays in step 2 equal the
rays in step 1.
-Extended rays (virtual) are dotted
2
Characteristics of images formed by plane
mirrors:
Images are:
-virtual
-upright
-equal to the size of the object
-the position is behind the mirror, at the
same distance from the mirror as the
object
3
Images formed by a pinhole camera
Images are:
-real
-inverted
-the size depends on the ratio between
the do (distance of object from pinhole)
and di (the distance of the screen from
the pinhole)
-the position is behind the pinhole
4
Magnification (size) of an image
can be found mathematically
M = hi/ho
hi = height of image
ho = height of object
M = - di/do
di =the distance of
the image from
mirror/lens
do= the distance of
the object from the
mirror/lens
If the object is inverted, the hi will be
negative
di is negative if the image is behind the
mirror
If magnification is negative it is because
the image is inverted (upside down)
5
Example: A pinhole camera with a depth of
20.cm is used to take a photograph of a person
standing 5.0 m away. If the height of the
image is 10. cm, what is the magnification (M)
of the pinhole camera and how tall is the
person?
List what you know and what you need to find
M=?
di = do = hi = ho= Write the two formulas:
M = - di /do (di is positive in a pinhole
camera)
M = hi/ ho
Plug in the values you have
M = - 0.20.m/5.0m
= -0.040m
Now we know M = -0.040m
-0.040 = hi/ho = 0.10m / ho
ho = 0.10m/-0.040m = 2.5m
6
Homework:
p. 70
1 ­ 6
7
Let's look at converging mirrors
8