Index of Refraction

Equations

Example 1#

Note:  ndiamond= 2.42 

1.24 x 108 m/s

Example 2#

Speed of light in water is 2.25x108 m/s (v). 

Determine the index of refraction. 

V

V = 2.25 x 108

C = 3.0x108

n = ?

n = C / V 

n = 3.0 x 10? / 2.25 x 108 = 1.33 

Example 3#

The refractive index of water is 1.33. The speed of light in water is?

• The critical angle is the angle of incidence which gives an angle of refraction of 90º.

• If you increase the angle of incidence past the critical angle, the refracted ray no longer exists the medium. This is called total internal reflection

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Applications / Examples of Total Internal Reflection

Fibre Optics

Triangular Prisms

• Exhibit total internal reflection.

• Reflect almost 100% of light internally.

Application of Triangular Prims

Retro-reflectors

• A retro reflectors is an optical device in which the emergent ray is parallel to the incident ray.

• They reflect light back the way it came.

• Occurs as a result of two internal reflections

• Applications of retro-reflectors include...

Retro-reflectors

• A retro reflectors is an optical device in which the emergent ray is parallel to the incident ray.

• They reflect light back the way it came.

• Occurs as a result of two internal reflections

• Applications of retro-reflectors include...

Triangular Prism

Also exhibits/displays total interal reflection. The critical angle for glass is about 41.1°.

If prims is oriented in such way that angle of incidence is greater than 41.1°, total internal reflection result. 

Prisms are so useful to reflect light that mirrors because a prism reflects almost 100% of light internally. Mirrors reflect most incident light but lose a little through absorption. Also, silvered surface of mirrors deteriorates over time. For these reasons, most optical devicees, such as cameras ad binoculars use prisms instead of mirrors. Emergent ray can be either 90° or 180° relative to incident rat, depending on placement of the prism.