# geo-2 - Geometric Optics Objective To study the basics of...

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Geometric Optics Objective: To study the basics of geometric optics and to observe the function of some simple and compound optical devices. Apparatus: Pasco optical bench, mounted lenses (f= +100mm, +200mm, -150mm), concave/convex mirror, mounted half-circle screen, unmounted convex lens, unmounted concave lens, unmounted concave/convex mirror, projection screen and paper, light source and powers supply, meter stick, ruler Introduction Optical instruments serve many functions. They can enlarge or magnify as in microscopes, making visible extremely small objects. Or, as in telescopes they can collect and concentrate light from very faint and distant objects. Or, they are used to form images that can be recorded as in photographic and video cameras. Optical elements depend on changing the direction of rays, by refraction (glass or plastic) or by reflection (mirrors). Some compound instruments combine both types. In geometric optics there is always an object (target) and an image. For reflective elements, the observer is on the same side as the object. On the other hand, light must pass through a refractive element; thus, the observer must be on the opposite side. Geometric optics uses light rays to calculate and analyze images. The true electromagnetic wave nature of light is ignored at first although the ultimate performance of the optical instrument is limited by the wave nature of light. Theory Since you have covered much of the theory in your lecture course, below we summarize some important equations that you will need in this lab: f =− 1 2 R The focal length of a convex mirror as it relates to its radius

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f = 1 2 R The focal length of a concave mirror as it relates to its radius m = h i h o =− d i d o Magnification is defined either as the ratio of the image and object heights, or as negative ratio of the image and object distances. Note that the magnification can either positive or negative; positive magnifications result in upright images and negative magnifications result in inverted images. The image distance can also be positive or negative, depending on whether it is real (can be projected onto a screen) or virtual (cannot be projected onto a screen), respectively. 1 d o 1 d i = 1 f This is the Thin Lens Equation. The sum of the reciprocal of the object and image distances equals the reciprocal of the focal length. This approximation assumes that the idealized lens or mirror has negligible width. All distances are therefore measured from the center of the actual lens or mirror. Note that the focal length can either be positive or negative depending on the lens being convex or concave, respectively. Also, the image distance is negative if the image is on the same side of the lens as the object. The image produced by a convex lens, which always converges light rays, doesn't always produce a
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geo-2 - Geometric Optics Objective To study the basics of...

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