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)