Geometrical optics

GEOMETRICAL OPTICS

DEFINITION.- Geometrical optics, or ray optics, describes light propagation in terms of “rays”. The “ray” in geometric optics is an abstraction, or “instrument”, which can be used to approximately model how light will propagate. Light rays are defined to propagate in a rectilinear path as far as they travel in a homogeneous medium.

Geometrical optics provides rules, which can depend on the color of the ray. Images are form the light rays converge which means come together. When they go straight to your eyes, you se images in the same spot as you see the object.

RAINBOWS.- It is an optical and meteorological phenomenon. That is caused by reflection of light in water droplets in the Earth’s atmosphere, resulting in the spectrum of light appearing in the sky. We see rainbows when the sun is behind us and falling rain is in front of us. We see them in arcs when in reality they are form as circles, they have no end, it usually occurs after it rains.

Why do we see the different colors?

Because there are different wavelengths of light. The colors are red, yellow, green, blue, indigo, and violet. We see red light from the higher drops because it is directed towards the observer’s eye. Violet light is directed above the level of the eyes. So we don’t see it.

TYPES OF RAINBOWS

PRIMARY.- We see all of the time. These are the normal red to violet arcs that we see after it rains.

SECONDARY.- are the rainbows that are reflected twice inside of the rain drop. They have the colors reversed and appear next to the primary rainbow.

FOGBOWS OR WHITE RAINBOWS.- They are sometimes seen in clouds and fogbanks.

LUNAR RAINBOWS.- Are formed when the moon emits white light that raindrops can refract and reflect into the atmosphere. Moonlight is much fainter than sunlight so a lunar rainbow is not very bright. This also appears as a white arc because we lose our light sensitivity at night so we cannot distinguish color.

References

AnnCroy, R. (2012). Rainbow. Retrieved from

http://ffden-2.phys.uaf.edu/211.web.stuff/croy_filla/Page_1.html

Geometric optics. (2013). Retrieved from

http://groups.physics.northwestern.edu/lab/optlens.pdf

...