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Spherical Mirrors
(A) Concave mirror: Mirror reflects from inner side of spherical surface
Point A – center of mirror called vertex Point C – center of curvature CFA – optic (principal) axis r – radius of curvature; F- focal point (focus)
Paraxial approximation: parallel light rays incident upon concave mirror are reflected through F if their height is less than r.
Focal length (FA) = f =
r 2 Image Formation-Ray Diagrams
Can use 3 light rays to find image of an object
When center of curvature C is on the same side as the outgoing (reflected) light, then radius of curvature r>0; otherwise, r<0.
P ray
F ray
C ray
(B) Convex mirror: Mirror reflects from outer side of spherical surface (Diverging mirror). Here r<0. So we have a negative focal length, f < 0, since r f 2
still holds.
Mirror equation still holds with both f and di negative.
Image is virtual and upright (di<0, m>0). Image is located on non-reflecting side of mirror and is located between A and F. Image is at F if object is at infinity.
Index of refraction
The velocity of light in media, such as water and glass, is slower than its velocity in vacuum, c=3.00x10^8 m/s.
Index of refraction: dimensionless material constant defined as the ratio of the velocity of light in free
space to its value in the medium: v
c n
From table 23-1: Velocity in light of ethyl alcohol (n=1.36) is:
s
m 0.74c 2.22x
c n
c v ^8
