Peoples Physics Concepts

16.4. Refraction http://www.ck12.org

16.4 Refraction

• Describe why light refracts when entering different substances like water and glass.


• Calculate the angle of refraction using Snell’s Law.

Students will learn why light refracts when entering different substances like water, glass, etc. and how to calculate

the angle of refraction using Snell’s Law.

Key Equations

c= 300 , 000 ,000 m/s ; the speed of light

n=uc

The index of refraction,n, is the ratio of its speed(c)in a vacuum to the slower speed(u)it travels in a material.n

can depend slightly on wavelength.

nisinθi=nfsinθf; Snell’s Law

Guidance

Fermat’s principle states that light will always take the path that takes the least amount of time (not distance).

Refraction follows from this. When light travels from air into another material (like glass), its speed through the

material is reduced due to interactions between photons that make up the light ray and the densely packed atoms of

the material. Because light is effectively moving slower in the glass, for example, as compared to air, the light ray

bends in order to get out quicker and satisfy Fermat’s Principle of least time. This is called refraction. The figure

below demonstrates the refraction a light ray experiences as it passes from air into a rectangular piece of glass and

out again.

Example 1