ch15_ty


 * 15-1 Refraction**

When light goes through one medium to another the speed of light changes depending on the factors of the media. When of light comes between two media, it will be reflected off and bent while going through the boundary between the two media. When a light ray bent and passes through a boundary, it is said that the ray is refracted.

An importantly property of transparent substances is the index of refraction. The index of refraction is the ratio of speed of light moving in a vacuum to the speed of light in a particular substance. By doing this, we can determine how fast light travel through certain media.

math \displaystyle n=\frac{c}{v} math

Note that use the value n=1.00 for air when solving refraction related problems.

The index of refaction of a material can be used to find out how a ray of light will refract and passes from one medium to amother. In 1621, Willebrord Snell conducted experiments with light passing through different media and formed the Snell’s law that describes the relationship between the two angle of incidence and refraction of light traveling from two media.

math n_i\sin\theta=n_i\sin\theta math

Practice: A light ray of wavelengh 589 nm traveling through airstrikes a smooth surface atan angle of 30.0 degree to the normal. Find the angle of refraction.

math n_i\sin\theta_i=n_i\sin\theta_r math math \theta_r=\sin^{-1} [\frac{(n_i)(\sin\theta_i)}{n_2}] math math \theta_r=\sin^{-1} [\frac{(1.00)(\sin30.0)}{1.52}] math math \theta_r=19.2 degree math


 * 15-2 Thin Lenses**

Lenses act the save as curved mirrors with a few differences: lenses have focal points on the two sides. When an object is in the front of the lens the sign is positive where its negative if it’s behind. The image is positive if it’s on the back of the lenses. The focal points are positive for converging lens and negative for diverging lens.

The same equations from the previous chapter:

math \displaystyle \frac{1}{p}+\frac{1}{q}=\frac{1}{f} math

math \displaystyle M=\frac{h}{h^1}=-\frac{q}{p} math

Rules for drawing the diagrams:


 * 1) A ray that comes in parallel to the principal axis and goes out through the focal
 * 2) Ray comes in through the focal and goes parallel to the principal axis
 * 3) Ray that goes straight through the center of the lens


 * 15-3 Optical Phenomena**

Total internal reflection can sometimes occure when light passes from a medium with a higher index of refraction than a lower one. To determine the ratio of the index of refraction of two mediums with a critical angle \Theta_c the expression is:

math \Sin\theta_c = \frac{n_r}{n_i} math math n_i>n_r math

Sometimes when light passes through the atmosphere, the wavelengths of the light can be scattered, and this phenomenon is known as Rayleigh scattering. Dispersion can occur if the boundary of a media refracts different wavelengths. When this occurs, a colorful “rainbow” can be seen, and chromatic aberration or the focusing of different colors by a lens at a distance behind the lens will result.

Sources: Faughn, Jerry S. and Raymond A. Serway. __Physics__. New York: Holt, 2004. Strong, Tom. Course notes. Honors Physics, Dept. of Science, Mount Lebanon High School. 2009.