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AP Physics IV.C
Geometric Optics
Wave Fronts and Rays
IV.C.1 Reflection of Light
Specular and diffuse reflection
IV.C.2 Plane Mirrors
Five Properties of the image of a
Plane Mirror
• Upright
• Same size
• Located as far behind the mirror as the
object is in front of the mirror
• Left to right reversed
• Virtual image
Ray Diagram for a Plane Mirror
Ex. What is the minimum mirror height needed for a person to see
their full image?
Spherical Mirrors (concave –
converging and convex –
diverging)
The focal length and radius of
curvature
Ray diagrams for curved mirrors.
Only two rays are needed to locate
an image
• Any ray drawn parallel to the principal axis is
reflected through the focal point
• Any ray drawn through the focal point is reflected
parallel to the principal axis
• Any ray incident upon the mirror is reflected at the
same angle when measured from the normal
• Any ray drawn through the center of curvature is
reflected upon itself
The mirror equation and
magnification (and an impressive
proof thrown in for free)
Summary of sign conventions for
curved mirrors
• f is positive for a concave mirror and
negative for a convex mirror
• so is positive for an image located in front of
the mirror (our only concern at this point)
• si is positive for a real image (in front of the
mirror) and negative for a virtual image
(behind the mirror)
Ex. A 2.00 cm object is placed 7.10 cm from a concave mirror
whose radius of curvature is 10.20 cm. Find the location and
size of the image.
Ex. An object with a height of 1.20 cm is placed 6.00 cm in front
of a concave mirror with a focal length of 10.0 cm. Find the
location and height of the image.
Ex. An object is placed 66 cm in front of a convex mirror that
has a focal length of 46 cm. Find the image distance and
magnification.
IV.C.3 Refraction and Lenses
Refraction – the bending of light as
it passes between two media with
different optical densities
Snell’s Law
Ex. Light is incident upon an equilateral crown glass prism at
an angle of 45.0º to one face. Calculate the angle at which the
light emerges from the opposite face.
Total Internal Reflection
Ex. A ray of light in a diamond (n = 2.42) strikes an interface at
28º. Will the beam of light enter the air or will it be reflected
internally? Will the beam of light be reflected internally if the
diamond is surrounded by water?
Applications of total internal
reflection
Dispersion of Light
Lenses
Two types of lenses
Images formed by converging lenses
Image formed by a diverging lens
A familiar friend
Sign conventions for lenses:
• f is positive for converging lenses and
negative for diverging lenses
• so is positive when light is reflected from
the object (a real object)
• si is positive when it is behind the lens
(real image) and negative when it is in
front of the lens (virtual image)