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Ch. 17 Reflection and Refraction. Milbank High School . Sec. 17.1 How Light Behaves at a Boundary. Objectives Explain the law of reflection Distinguish between diffuse and regular reflection and provide examples Calculate the index of refraction in a medium. The Law of Reflection.
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Ch. 17 Reflection and Refraction Milbank High School
Sec. 17.1How Light Behaves at a Boundary • Objectives • Explain the law of reflection • Distinguish between diffuse and regular reflection and provide examples • Calculate the index of refraction in a medium
The Law of Reflection • Smooth Surfaces • Mirrors • Angle of incidence = angle of reflection • Seemingly smooth surfaces • Walls • Paper • Actually rough surfaces • Light waves result in diffuse reflection
Refraction of Light • Refraction • Change in direction or bending of light at the boundary of two media • Plastics, glass • Optically dense materials • If angle of refraction is smaller than the angle of incidence
Snell’s Law • The degree of refraction depends on angle of incidence and properties of the medium • Snell’s Law • Ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant
Index of Refraction and the Speed of Light • Index of refraction • Measure of how much light bends in a new medium • It bends because of a change in speed • Index of refraction nsubstance = c/vsubstance
Review Questions • Could the index of refraction ever be less that 1? • What behaviors does light exhibit?
Sec. 17.2Applications of Reflected and Refracted Light • Objectives • Explain total internal reflection • Define the critical angle • Explain effects caused by the refraction of light in a medium with varying refractive indices • Explain dispersion of light in terms of the index of refraction
Total Internal Reflection • Occurs when light passes from a more optically dense medium to a less optically dense medium at an angle so great that there is no refracted ray • Critical angle • The incident angle that causes the refracted ray to lie right along the boundary of the substance, angle Θc sin Θc = nr/ni
Effects of Refraction • Mirages • Index of refraction changes in hot air vs. cool air • Sunlight after the sun has set • Index of refraction changes due to the change in density of the atmosphere
Dispersion of Light • Separation of light into its spectrum • Happens as light travels through a prism • Glass • Diamonds • Water • Red bent the least • Violet bent the most
Rainbows • Spectrum formed when sunlight is dispersed by water droplets in the atmosphere • In afternoon, only see rainbows to the east