Ch. 17 Reflection and Refraction Milbank High School

Sec 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 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 n substance = c/v substance

Review Questions Could the index of refraction ever be less that 1? What behaviors does light exhibit?

Sec Applications 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 Θ c sin Θ c = n r /n i tro_physics/kisalev/java/totintrefl/index.h tml

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

White light separates into different colors (wavelengths) on entering the raindrop because red light is refracted by a lesser angle than blue light. On leaving the raindrop, the red rays have turned through a smaller angle than the blue rays, producing a rainbow.

Sun Dog Refraction of sunlight by ice crystals Cirrus or cirrostratus clouds