Magnifications in Mirrors & Lenses
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A measure of how much larger or smaller an image is
compared with the object itself.
Magnification = image height
object height
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or image distance
object distance
M = hi
or
M = - di
ho
do
The numbers can be obtained by measurement with a ruler or
be given to you
Magnification does not have any units but make sure you use
the same units for height or distance!
Parameters
OBJECT
IMAGE
ho
MIRROR
hi
do
di
NOTE: positive and negative signs are used to
give information about direction in physics


di is negative if you have a virtual image
If your image is inverted then height and
magnification are NEGATIVE
Orientation of
image with
respect to object
Sign of M
Type of image
Upright
+
Virtual
Inverted
-
Real

A concave shaving mirror has an object that
is 93 cm tall placed in front of it. The image
produced is upright and 51 cm tall . What is
the magnification of the mirror?

A pencil is placed 25 cm in front of a concave
mirror. It produces an inverted image that is
12.5 cm from the mirror. What is the
magnification of the mirror?

A mirror has a magnification of 15. If the
object placed in front of it is 2cm tall, what is
the height of the image?

The magnification of a mirror that produces
an inverted image is 7. How far away was the
object placed from the mirror if the image
produced is 2.5 cm away?


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A thin lens is a lens with a thickness (distance
along the optical axis between the two surfaces
of the lens) that is negligible compared to the
radii of curvature of the lens surfaces.
Lenses whose thickness is not negligible are
sometimes called thick lenses.
Thin lens equation= 1/f = 1/do +1/di
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