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Ray Optics: Reflection and Refraction 10.1 Rays • Representation of the path that light follows • Represent beams of light that are composed of millions of light photons traveling together Reflection • When a light ray strikes the surface of a material and some of the light bounces off the surface Reflection • Normal line – Perpendicular to the surface at the point of reflection • Angle of incidence – The angle between the incoming light ray and the normal line • Angle of reflection – The angle between the normal line and the reflected ray. Reflection • The angle of incidence is always equal to the angle of reflection Reflection • Flat mirrors – Plane mirrors – Produces an image that is reversed and appears to be located the same distance behind the mirror as the object is in front of the mirror Reflection • Spherical mirrors – Convex • Outside surface (back) of a spoon – Concave • Inside surface (front) of a spoon Reflection • Focal Point of a Flat Mirror – The point in front of the mirror at which the reflected rays all meet • Spherical mirrors or lenses do not have exact focal points. – Focal point of a concave mirror is in front of the mirror – Focal point of a convex mirror is behind the mirror Reflection • Real image – Formed by a mirror or lens when light rays from the object converge. It can be seen by placing a screen or piece of paper at the point at which the light from the object converges. • Virtual image – Apparently causes light to diverge from a mirror or lens. It cannot be seen on a screen or piece of paper since no light actually converges at the image location. Refraction • The change in direction of a wave or photon of light as it crosses a boundary into a different medium • Index of refraction is the ratio of the speed of light in a vacuum to the speed of light in the material Total Internal Reflection • When the angle of refraction is greater than 90º, a light ray is reflected. • Optical fibers – Light stays in the fiber because each interaction of the light bouncing off the side is reflected Lenses • A carefully ground or molded piece of transparent material • Convex lens—thicker at its center than at its edges (converging) • Concave lens— thinner at its center than at its edges (diverging)