Refraction Snells Law Relative index Consider ni sin

Refraction - Snell’s Law - Relative index Consider: ni sin Øi = nr sin Ør Absolute index of refraction of incident medium refracted medium If We: sin Øi / sin Ør = nr / ni Then: nr / ni = nri * This is called the relative index of refraction

Øi ni Ø r nr The RELATIVE INDEX of refraction is the ratio of the 2 indices of refraction of the 2 media. nr / ni = nri

Problems - index of refraction. ns = C/Vs #1. If the speed of light in plastic is 2. 00 x 108 m/s, what is the index of refraction of the plastic? ns = C/Vs ns = 3. 00 x 108/2. 00 x 108 ns = 1. 50

#2. A block of unknown material is submerged in water. Light in the water is incident on the block at an angle of 31º. The angle of refraction is 27º. What is the index of refraction of the unknown material?

Øi Water 1. 33 Ør ni sin Øi = nr sin Ør 1. 33 sin 31 = nr sin 27 Material ? 0. 6850006 = nr 0. 4539905 1. 51 = nr What is the speed of light in this material? ns = C/ Vs Vs = C/ ns = 3. 00 x 108/1. 51 = 1. 99 x 108 m/s

Total Internal Reflection (TIR) We know that when light travels into a less dense medium it bends away from the normal. If the angle of incidence is increased enough then the refracted ray will emerge along the boundary between the 2 media. This is called Total Internal Reflection.

Øi = Ør Air Øi Water Øc Find Øc , the critical angle. ni sin Øc = nr sin 90 1. 33 sin Øc = 1. 00 (1. 00) sin Øc = 0. 7519797 Øc = 48. 8º

Now find Øc for Crown Glass and Air. Sin Øc = nr sin Ør / ni sin Øc = (1. 00) sin 90º / (1. 52) sin Øc = 1/1. 52 Øc = 41. 1º = 0. 6578947

The Critical Angle is the incident angle at which the refracted light is emitted such that it travels along the boundary between the media. This Critical Angle is different for each combination of media. Applications: Fiber Optics. When a long thin tube of glass is made such that light sent in one end makes contact with the sides at angles greater than Øc then TIR occurs.

Fiber Optics: - Converts analog signal to digital. - Uses bits of information, “ 0” & “ 1” - 25, 000 telephone conversations can be simultaneously transmitted in an optic fiber the thickness of a human hair. Ex. Telephone wires, computer networking, medicine, plants!!

Refraction - superior/inferior mirage. Superior mirage. Apparent eye Cold Surface Actual Object Light bends back down as it hits warmer air and, because it is less optically dense, the light bends away from the normal. To you objects such as islands appear in the sky.

Inferior Mirage Warm road Real object Apparent object Light travelling towards the ground meets warm air and bends away from the normal, turning it back upwards so an image is formed on the pavement. This is why you see a mirror or water on the road with images in it.