Question

Partner: Date Name 11 Snell's Law Introduction When light passes from one material to another it is always bent away from its original path. This process is known as refraction and the change in direction depends on the change in optical density (or refractive index) of the two materials. A larger change in refractive index results in a larger change in angle between incoming and outgoing light beams. A light beam bends closer to the normal in the material with the higher refractive index, as shown in Fig 1. The relationship between the angles of the incident and refracted light beams is given by Snell's Law where θ, is the angle of incidence, θ/2 is the angle of refraction, and ni and n2 are the indices of refraction for each material. The angles of incidence and refraction are measured with respect to the normal, which is the line perpendicular to the boundary between the materials. For a boundary between materials such that n2 <nI (the light is being refracted into a material with a smaller index of refraction than the one it is leaving), there will be a critical angle θ° o, such that θR = 90 . Once the angle of incidence exceeds the light will be unable to leave the material. This is known as total internal reflection and is responsible for the the reason dia- monds (with n 2.4) seem to sparkle on their own. ni Fig. 1: Snell's Law at interface The velocity of a light beam is always slower in materials with a higher refractive index. Because all materials have a refractive index larger than air (nair 1 while nwater 1.33 for example). light always travels slower in these materials. The index of refraction for a material is defined as n - c/v, where c is the speed of light in air and v is the speed of light in the material. Experiment . Equipment: Optics bench, light source, ray table with base, slit plate, slit mask, component holder, semicircular glass block, parallel ray lens . Mount the parallel ray lens on the light source. 67

Answer 1

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