total internal reflection

TOTAL INTERNAL REFLECTION Lesson 9

SNELL’S LAW

The phenomenon of refraction had been observed for centuries, but it was not until 1621 that its cause was stated mathematically.

SNELL’S LAW

Willebrord Snell (1591–1626) was a Dutch astronomer and mathematician who is credited with identifying the exact relationship between the angle of incidence and the angle of refraction.

SNELL’S LAW

Snell’s law is a formula that uses values for the index of refraction to calculate the new angle that a ray will take as a beam of light strikes the interface between two media.

SNELL’S LAW

If you call the indices of refraction of the two media n1 and n2 and call the angles of incidence and the angle of refraction θ1 and θ2, then the formula for Snell’s law is:

n1sinθ1 = n2sinθ2

TOTAL INTERNAL REFLECTION

Sometimes, such as in the case of fibre optics, light does not pass from one medium to another but stays within the medium.

TOTAL INTERNAL REFLECTION

In total internal reflection, light reflects completely off the inside wall of a denser medium (higher index of refraction) rather than passing through the wall into a less dense medium (lower index of refraction).

TOTAL INTERNAL REFLECTION

Recall that when light passes from a denser material, such as water, into a less dense medium, such as air, the light refracts away from the normal.

TOTAL INTERNAL REFLECTION As the angle of incidence increases, the

angle of refraction increases. At a certain angle, called the critical angle, the refracted ray of light follows a path exactly along the surface of the water. Even though the light refracts, it does not leave the water. In a way, the light is “trapped” inside the water

TOTAL INTERNAL REFLECTION When light crosses a boundary

between materials with different indices, the light beam will be partially refracted at the boundary surface, and partially reflected.

MIRAGES

Both total internal reflection and refraction play a role in forming a mirage.

A mirage is an image of a distant object produced as light refracts through air of different densities.

MIRAGES

Since the light rays pass through layers of air with progressively lower indices of refraction, eventually the light is totally internally reflected.

INDEX OF REFRACTION - LAB