Transcript Formation of Images by Spherical Mirrors

Formation of Images by
Spherical Mirrors
For an object infinitely far away (the sun or starts), the rays
would be precisely parallel.
If a mirror is small compared to its
radius of curvature, so that the reflected
rays make only a small angle upon
reflection, then the rays will cross each
other at a single point, or focus.
The principal axis of a mirror is defined as the
straight line perpendicular to the curved
surface at its center.
The point F, where the rays parallel to the
principal axis, come to a focus, is called
the focal point of the mirror.
The distance between focal point and the
center of the mirror is called the focal
length, f, of the mirror.
Another way of defining the focal point is
to say that it is the image point for an
object infinitely far away along the
principal axis.
Finding the Image Position for a
Curved Mirror
-ray 1 is drawn parallel to the axis; therefore it must pass
along a line through F;
-ray 2 is drawn through F, as result is must reflect into parallel
to the principal axis ray;
-ray 3 is chosen to be perpendicular to the mirror, and so is
drawn so that it passes through C, the center of curvature; it
will be reflected back on itself.
Mirror Equation
1
1 1
 
d o di f
The lateral magnification, m, of a mirror is
defined as the height of the image divided by
the height of the object:
hi
di
m

ho
do
The Sign Convention
-the image height hi is positive if the image is
upright, and negative if inverted, relative to the
object;
-di and do are both positive if image and object are
on the reflecting side of mirror, but if either image
or object are behind the mirror, the corresponding
distance is negative.