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Total Internal Reflection • Special case of Refraction! Refraction of Light • Example Problem #2 A ray of light enters the air from the water at an angle of 50 degrees. What is the angle of refraction? Refraction of Light • Example Problem #2 A ray of light enters the air from the water at an angle of 50 degrees. What is the angle of refraction? n1 = 1.33 Refraction of Light • Example Problem #2 A ray of light enters the air from the water at an angle of 50 degrees. What is the angle of refraction? n1 = 1.33 θ1 = 50 degrees Refraction of Light • Example Problem #2 A ray of light enters the air from the water at an angle of 50 degrees. What is the angle of refraction? n1 = 1.33 θ1 = 50 degrees n2 = 1 θ2 = ? Refraction of Light • Example Problem #2 A ray of light enters the air from the water at an angle of 50 degrees. What is the angle of refraction? n1(sin θ1) = n2(sin θ2) Refraction of Light • Example Problem #2 A ray of light enters the air from the water at an angle of 50 degrees. What is the angle of refraction? n1(sin θ1) = n2(sin θ2) 1.33(sin 50) = 1 (sin θ2) Refraction of Light • Example Problem #2 A ray of light enters the air from the water at an angle of 50 degrees. What is the angle of refraction? n1(sin θ1) = n2(sin θ2) 1.33(sin 50) = 1 (sin θ2) θ2 = Error Refraction of Light • Example Problem #2 When you get error on your calculator, this means something. This means that the light does NOT refract (enter the new medium), it must do something else. Refraction of Light • Let’s take a look at what happens as we increase the angle of incidence Refraction of Light • Let’s take a look at what happens as we increase the angle of incidence Refraction of Light • Look what happens to the ray at this specific angle? Refraction of Light • Where do you think the light ray goes in the right hand diagram??? Refraction of Light • It does not enter the new medium, it reflects off the surface (like skipping a stone on the water) Refraction of Light • This phenomenon is called TOTAL INTERNAL RELFECTION Total Internal Reflection • This occurs when you get ‘Error’ on your calculator. Total Internal Reflection Total Internal Reflection Total Internal Reflection • This is also how fiber optics works. The light is trapped inside. Fiber Optics • Fiber optics (optical fibers) are long, thin strands of very pure glass about the diameter of a human hair. – They are arranged in bundles called optical cables and used to transmit light signals over long distances. • If you look closely at a single optical fiber, you will see that it has the following parts: – Core - Thin glass center of the fiber where the light travels – Cladding - Outer optical material surrounding the core that reflects the light back into the core – Buffer Coating - Plastic coating that protects the fiber from damage and moisture Fiber Optics • The light in a fiber-optic cable travels through the core by constantly bouncing from the cladding due to total internal reflection. – Because the cladding does not absorb any light from the core, the light wave can travel great distances. Total Internal Reflection • This is what gives a diamond its luster. The light gets trapped inside the diamond and is only allowed to escape at certain angles! Diamonds are a Physicists Best Friend •The cut of the diamond must be just right to get reflection from the bottom facet. •Too Shallow •It Leaves •Too Deep •It Leaves •Now it’s just right Total Internal Reflection • The surface acts like a mirror so it will bounce off at the same angle it comes in at. Critical Angle • What is the angle of incidence which is the boundary between refraction and total internal reflection? Critical Angle • This angle is called the CRITICAL ANGLE Critical Angle • Let’s calculate the critical angle (incidence angle) when going from water to air. θ2 n (air) = 1 θc n (water) = 1.33 Critical Angle n1 = 1.33 θc=? n2 = 1 θ 2= 90 θ2 n (air) = 1 θc n (water) = 1.33 Critical Angle n1(sin θc) = n2 (sin θ2) Critical Angle n1(sin θc) = n2 (sin θ2) 1.33 (sin θc) = 1(sin 90) Critical Angle n1(sin θc) = n2 (sin θ2) 1.33 (sin θc) = 1(sin 90) 1.33 (sin θc) = 1(1) Critical Angle n1(sin θc) = n2 (sin θ2) 1.33 (sin θc) = 1(sin 90) 1.33 (sin θc) = 1(1) (sin θc) = 1/1.33 Critical Angle n1(sin θc) = n2 (sin θ2) 1.33 (sin θc) = 1(sin 90) 1.33 (sin θc) = 1(1) (sin θc) = 1/1.33 θc = 48.8 degrees Critical Angle • So the equation ends up being Sin өc = n2 n1 Critical Angle • The critical angle when going from water to air is 48.8 degrees θ2 n (air) = 1 θc n (water) = 1.33 Critical Angle • This means if our angle of incidence is less than 48.8 degrees, we will get refraction. Critical Angle • This means if our angle of incidence is greater than 48.8 degrees, we will get total internal reflection. Homework • Do worksheet #2 in minipacket