Refraction

"Technology...the knack of so arranging the world so that we need not experience it"
Max Frisch

Refraction may be defined as the "bending" of light (or any EM wave) as it passes from one medium to another. The bending is caused by differing speeds of the wave in the two media.

Refractive Index
The refractive index, n, of a medium is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium
Snell 's Law (Law of Refraction), describes exactly how much the light is bent when passing from one medium to another.

Snells law

$Refraction picture$

Important points

Light is bent towards the normal when moving into a medium of larger refractive index.

Angles of incidence, reflection and refraction are all measured with respect to the normal.

As a general rule the refractive index increases with the density of the medium. For example, the refractive index of glass (1.5) is greater than that of water (1.33) - glass is more dense than water.

Light incident normally is not deflected.

Light rays are "reversible". In other words the refracted ray in the above diagram can act as an incident ray and the incident ray will represent the direction of the refracted ray.

The refractive index of a medium depends on the wavelength of light, e.g. in glass, blue light travels more slowly than red light. This phenomena is called "dispersion".

What is π?
Mathematician: "π is the ratio of the circumference of a circle to its diameter."
Engineer: "π is about 22/7."
Physicist: "π is 3.14159 plus or minus 0.000005."
Computer Programmer: "π is 3.141592653589 in double precision."
Nutritionist: "You one track math-minded fellows, Pie is a healthy and delicious dessert!"

Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu