PHYA22 Chapter 23.doc

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University of Toronto Scarborough
Physics and Astrophysics
Brian Wilson

Chapter 23 Ray OpticsThe Ray Model of LightLight Ray a line in the direction along which light energy is flowingA laser beam is a bundle of many parallel light raysRay Model of LightoLight rays travel in straight lines where vcn where n is the index of refractionoLight rays can cross two rays can cross without either being affected in any wayoA light ray travels forever unless interacts with matter which causes the light ray to change direction or to be absorbedAt an interface between two materials light can be reflected or refractedWithin a material light can be scattered or absorbedoAn object is a source of light rays they originate from every point on the object and each point sends rays in all directionsoThe eye sees by focusing a diverging bundle of rays from each point on the object enter the pupil and are focused to an image on the retinaObjects can be selfluminous or reflectiveLight rays exist independently of whether you are seeing themDiverging rays from a point source are emitted in all directionsRay Diagram showing only a few rays leaving the top and bottom points of the object and traveling to the rightAperture a hole through which light passesoEach point on an object emits light rays in all directions but only a very few of those rays pass through the aperture and reach the back wallohihodido where do is the distance to the object and di is the depth of the camera obscura dido so the image is smaller than the objectReflectionSpecular Reflection reflection from a flat smooth surface like a mirror or polished metalqi between the ray and a line perpendicular to theAngle of Incidencesurface the normal to the surfaceAngle of Reflection qr the angle between the reflected ray and the normal to the surfaceLaw of ReflectionoThe incident ray and the reflected ray are the same plane normal to the surfaceoThe angle of reflection equals the angle of incidence qrqiDiffuse Reflection each ray obeys the law of reflection at that point but the irregular surface causes the reflected rays to leave in many random directionsFor a plane mirror the distance s to point P is equal to the object distance s ssVirtual Image if rays diverse from an object point P and interact with a mirror so that the reflected rays diverge from point P and appear to come from P P is a virtual image of PRays from each point on the object spread out in all directions and strike
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