Refraction Lenses Created by Stephanie Ingle Kingwood High

Refraction & Lenses Created by Stephanie Ingle Kingwood High School

Snell’s Law incident ray Boundary normal Air (n=1. 0003) 1 2 reflected ray Water (n= 1. 33) n = index of refraction for medium (no units) • Angles are always measured from the normal, never the surface •

Index of Refraction • Light changes speed (v) as it enters a new medium • In a vacuum the speed of light (c) is 3. 0 x 108 m/s • The index of refraction (n) of a material is the ratio of the speed of light in a vacuum to the speed of light in the material. • Index of refraction has no units!

Critical Angle • The incident angle of light n=1 that causes refraction along 0 =90 qr the boundary between surfaces qc n=1. 5 • The angle of refraction will always be 90 o • Only possible when going from more optically dense (high index of refraction) to less optically dense medium (low index of refraction • Only possible when light speeds up as it passes through the boundary

Total Internal Reflection • When incident light strikes a boundary at an angle greater than the incident angle it does not cross the boundary into the new medium. • Instead, all of the light is reflected from the boundary back into the original medium according to the Law of Reflection.

Concave Lenses • Thicker at the edges than in the center • Parallel rays of light from a far object will refract throught the lense and diverge as if they came from the focal point. • Concave lenses also called “diverging lenses” • Light may come in from either side of lens so there will be a focal point on both sides equal distances from the lens (assuming symmetrical lenses).

Convex Lenses • Thicker in the center than at the edges • Parallel rays of light from a far object will refract through the lens and converge at the focal point. • Convex lenses also called “converging lenses” • Light may come in from either side of lens so there will be a focal point on both sides equal distances from the lens (assuming symmetrical lenses).

Calculations f = focal length do = object distance di = image distance hi = image height ho = object height M = magnification

Interpreting Calculations Focal length (f) converging, then f = + diverging, then f = - Image distance (di) di=+ , then image is real do= -, then image is virtual Magnification (M) M = +, image is erect M = - , image is inverted

Ray Diagram Convex Lens Draw 3 rays from tip of object: 1) parallel, then through f 2) through f, then parallel 3) through the lens at the principal axis Image is real, inverted, & reduced f f

Ray Diagram Draw 3 rays from tip of object: 1) parallel, then through f Convex Lens (Inside f) 2) from same side f, through tip of object, then parallel 3) through the lens at the principal axis image f f object Image is virtual, erect, & magnified

Ray Diagram Draw 3 rays from tip of object: Concave Lens 1) parallel, then refracted ray from f on same side of lens 2) to lens along a line that would pass through f on the other side of lens, then parallel 3) through the lens at the principal axis concave lens (axis) object image Image is virtual, erect, & reduced f f