Transcript Ray Optics: Reflection and Refraction

Ray Optics: Reflection and
Refraction
10.1
Rays
• Representation of the path that light
follows
• Represent beams of light that are
composed of millions of light photons
traveling together
Reflection
• When a light ray strikes the surface of a
material and some of the light bounces off
the surface
Reflection
• Normal line
– Perpendicular to the surface at the point of
reflection
• Angle of incidence
– The angle between the incoming light ray and
the normal line
• Angle of reflection
– The angle between the normal line and the
reflected ray.
Reflection
• The angle of
incidence is always
equal to the angle of
reflection
Reflection
• Flat mirrors
– Plane mirrors
– Produces an image that is reversed and
appears to be located the same distance
behind the mirror as the object is in front of
the mirror
Reflection
• Spherical mirrors
– Convex
• Outside surface (back) of a spoon
– Concave
• Inside surface (front) of a spoon
Reflection
• Focal Point of a Flat Mirror
– The point in front of the mirror at which the
reflected rays all meet
• Spherical mirrors or lenses do not have
exact focal points.
– Focal point of a concave mirror is in front of
the mirror
– Focal point of a convex mirror is behind the
mirror
Reflection
• Real image
– Formed by a mirror or lens when light rays
from the object converge. It can be seen by
placing a screen or piece of paper at the point
at which the light from the object converges.
• Virtual image
– Apparently causes light to diverge from a
mirror or lens. It cannot be seen on a screen
or piece of paper since no light actually
converges at the image location.
Refraction
• The change in
direction of a wave or
photon of light as it
crosses a boundary
into a different
medium
• Index of refraction is
the ratio of the speed
of light in a vacuum to
the speed of light in
the material
Total Internal Reflection
• When the angle of
refraction is greater
than 90º, a light ray is
reflected.
• Optical fibers
– Light stays in the fiber
because each
interaction of the light
bouncing off the side
is reflected
Lenses
• A carefully ground or
molded piece of
transparent material
• Convex lens—thicker
at its center than at its
edges (converging)
• Concave lens—
thinner at its center
than at its edges
(diverging)