11.2 Partial Refraction and Total Internal Reflection - …sciencewithz.weebly.com/uploads/2/5/1/0/25106439/11.2_partial... · Partial Reflection and Refraction! When light travels

11.2Partial Refraction and Total Internal

Reflection

Partial Reflection and Refraction§ sometimes when you look out a window, you see what is outside as well as your own reflection

Partial Reflection and Refraction§ When light travels from one medium to another, some of the light is reflected and some is refracted

§ The amount of reflection compared with the amount of refraction depends on:

§ the angle of incidence§ the index of refraction of the two media

§ more light is refracted than reflected as indicted by the thickness of the rays

§ If the angle of incidence is nearly zero (light is traveling directly toward the water), very little light is reflected (most is refracted)

§ As the angle of incidence increases, more light is reflected and less refracted

Light Traveling from Air to Water

SUN OVERHEAD very little reflection, most light is refracted

SUNSET (close to horizon)most of the light is reflected (blinding)

small angle of incidence large angle of incidence

§ When you are underwater, you can only see the light that reaches you from an area directly above

Reflection and Refraction Underwater

§ Light coming from the area directly above you will refract and be visible to you

§ As the angle of incidence increases, more of the light reflects, less refracts (and less is visible to you)

Reflection and Refraction Underwater

Critical Angle

§ To see an object underwater, light must hit the object, reflect off it, and travel to your eyes

§ The water is clear, but you can see objects under water only when they are close to you. WHY?

Critical Angle

§ The incident rays are going from water to air, the refracted rays bend away from the normal

§ As the angle of incidence increases, the angle of refraction increases more rapidly

§ As the angle of incidence continues to increase, the angle of refraction will eventually reach 90°

Critical Angle§ The angle of incidence that produces an angle of

refraction of 90�

§ At this angle of incidence, the refracted ray lies along the boundary between water and air

§ No light passes into the air

Total Internal Reflection§ when incident light is not refracted but is entirely

reflected back from the boundary.

§ only occurs when light travels from a medium in which its speed is lower to a medium in which its speed is higher)

§ all the light is reflected back into the firstmedium (water)

Total Internal Reflection

Changing the Direction of a Light Ray

§ the critical angle between glass and air is less than 45°

§ light hitting an inner surface at exactly 45° will be totally reflected inside the glass

§ when light enters at one of the short sides of the prism, the direction of light is changed 90°

§ each hexagon functions like a prism to reflect light directly back in the direction it came from

Applications of Total Internal Reflection

RETROREFLECTORS

§ when the fibre is bent, the light is totally internally reflected along the entire fibre until it reaches the other end

Applications of Total Internal Reflection

OPTICAL FIBRES

§ telephone § cable television§ data transmission

Uses of Optical Fibres in Telecommunications

§ any one of these copper bundles can be replaced with one fiber strand

§ endoscopy - diagnostic procedure used to assess the interior surfaces of an organ by inserting a tube into the body

Uses of Optical Fibres in Medicine

Homework§ Read p. 457-466 in the textbook #1-5,7-8§ Complete “Section 11.2 Review” Worksheet