5 Total Internal Reflection Interference Diffraction and Refraction

5. Total Internal Reflection Interference, Diffraction and Refraction

Learning Intentions �Investigate the phenomenon of Total Internal Reflection �Investigate practical applications of TIR �Calculate critical angles for material of varying refractive index Success Criteria: By the end of the lesson I should be able to… �State why Total Internal Reflections occurs �State one practical use of TIR �State the definition of the critical angle and calculate its value based on the refractive index of different materials.

Activity Using the equipment provided measure the angle of refraction using the following diagram and table. Angle of incidence 10 o 20 o 30 o 40 o 50 o 60 o 70 o Angle of refraction

Results What did you notice about your results? Were there any problems in recording your results? Can you explain what happened?

Total Internal Reflection Because the angle of refraction in the air is always greater than the angle of incidence in the glass, there is a maximum angle of incidence that allows the ray to refract out of the glass.

Total Internal Reflection �

The Critical Angle �The critical angle of a material is determined by its refractive index. �The critical angle or refractive index can be found using Snell’s law: If the 2 nd material is air then n 2=1 and sinθ 2=sin(900)=1

Example �Now calculate the critical angle of the following materials:

Example Diamond Why are they so sparkly? Lead Sulphide

Applications of TIR: Optical Fibres Optical fibres are used in medical equipment such as endoscopes and for telephone & internet connections. Light travels through an optical fibre by total internal reflection.

Applications of TIR: Rainbows occur due to total internal reflection of sunlight within spherical water droplets. As the sunlight leaves the water droplet it refracts with each of the 7 colours that make up white light refracting different amounts. This causes a spectrum to be seen and is known as dispersion.

Applications of TIR: Rainbows

Uses for TIR Can you think of any uses for the property of TIR? Fibre optic cables used for: -Telecommunications -Local area networks -Cable TV -CCTV -Astronomy Optical fibre sensors used for: -endoscopes/ fibroscopes -Laparoscopic/ arthroscopic surgery Prismatic optical instruments Reflective panels for: -Clothing -Headlights -Bike reflectors -Road catseyes

Uses for TIR Can you think of any uses for the property of TIR? Use the internet to write a short paragraph on one particular use of TIR. You should include where appropriate a diagram and explanation of the physics involved. You should comment on the refractive index and critical angle of materials that are used.

Questions 6. Refraction of Light Q 8 -11