Wave Fronts and Rays
Physics 11
Reflection of Light:
Mirrors
Wave Fronts
Law of Reflection
Types of Reflection
Plane Mirrors
Spherical Mirrors
Ray Tracing
Wave Fronts and Light Rays
⇒ Wave fronts are surfaces that are in the same phase of
motion.
⇒ Rays are radial lines pointing outward from the
source and perpendicular to the wave fronts.
Law of Reflection
⇒ The incident ray, the
reflected ray, and the normal
to the surface all lie in the
same plane.
⇒ At large distances from the source, the wave fronts
become flat surfaces known as plane waves.
⇒ The angle of incidence equals the angle of reflection:
θi = θ r
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Specular Reflection
Diffuse Reflection
Plane Mirror
Plane Mirror
⇒ The image from a plane mirror is upright, the
same size as the object, and as far behind the mirror
as the object is in front of it.
⇒ The image from a plane mirror is virtual.
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Plane Mirror
Plane Mirror
⇒ To view one’s full
length in a mirror, only a
half-length mirror is
needed.
Spherical Mirrors
Concave and Convex Mirrors
Concave Mirror
Convex Mirror
⇒ A spherical mirror has the shape of a
section from the surface of a sphere.
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Image Point
Focal Point
f=½R
⇒ Light rays from a source cross at a common point
(called the image point) after reflection from a concave
mirror.
⇒ If the light rays are parallel to the principal axis, they
cross at a special point called the focal point F.
⇒ The distance from the center of the mirror to the focal
point is called the focal length f.
Spherical Aberration
Convex Mirror
f=-½R
⇒ Only light rays close to the principal axis (paraxial
rays) cross the focal point.
⇒ For a convex mirror, parallel paraxial rays appear to
originate from the focal point F.
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Ray Tracing
Ray Tracing
Ray 1: A ray initially parallel to the principle
axis will be reflected through the focal point.
Ray 2: A ray passing through the focal point
will be reflected parallel to the principal axis.
Ray Tracing
Images from a Concave Mirror
Ray 3: A ray that travels along a line that
passes through the center of curvature C be
be reflected upon itself.
⇒ A object placed between C and F will
produce a real, enlarged, inverted image beyond
the center of curvature C.
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Images from a Concave Mirror
Images from a Concave Mirror
⇒ A object placed beyond C will produce a
⇒ A object placed between F and the mirror
real, reduced, inverted image between C and F.
will produce a virtual, enlarged, upright image.
Images from a Convex Mirror
⇒ The image produced by a convex mirror is
always virtual, reduced, and upright.
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