-Atmospheric Refraction -Total Internal Reflection -Prisms and Rainbows -Total Internal Reflection

Atmospheric Refraction

Atmospheric Refraction Just like sound, light travels faster through hot air than cool air. The speeding up of the part of the wave nearest the ground produces a gradual bending of light rays.

Atmospheric Refraction The Sunset

Atmospheric Refraction At sunset, you can still see the sun after it is really below the horizon. The Earth’s atmosphere refracts (bends) the light. Every day, we get about 5 minutes of daylight more than we should.

Dispersion in a Prism In a prism, different frequencies of light travel at different speeds. Red travels faster than blue light. So different frequencies (colors) refract differently and bend at different angles.

Dispersion in a Prism Dispersion: The separation of light into colors arranged according to their frequency.

The Rainbow Caused by dispersion of light by raindrops.

The Rainbow When you move, your rainbow moves with you. Only you can see your rainbow.

Total Internal Reflection Total Internal Reflection: the reflection of all the light that strikes the boundary between two media. This will happen at the “Critical Angle.”

Total Internal Reflection Critical Angle: the angle in which a beam of light will reflect off of a boundary instead of transmit. Water has a critical angle of 48o. So if light within the water is more than 48o from the normal, the light will be totally internally reflected.

Total Internal Reflection

Total Internal Reflection Optical Fibers (light pipes) Use total internal reflection to “pipe” light from one place to another.

Lenses Converging and Diverging Lenses Image Formation by a Lens Constructing Images Through Ray Diagrams Image Formation Summarized

Lens A piece of glass that bends parallel rays of light so they cross and form an image. Principal Axis: the line joining the centers of curvature of its surfaces. Focal Length: the distance between the center of a lens and either focal point.

Converging (Convex) Lens A lens that bends incoming parallel rays so they converge to a single point. They are thicker in the middle than on the edges. Converging Focal Point: the point at which a beam of parallel light converges. Converging Focal Plane: the plane that passes through the focal point (perpendicular to the principal axis) where light can converge.

Diverging (Concave) Lens A lens that bends incoming parallel rays so they diverge from a single point. They are thinner in the middle than on the edges. Diverging Focal Point: the point from which the beam of light seems to come. Diverging Focal Plane: a beam appears to come from a point on a focal plane.

Image Formation by a Lens