| Mirrors are objects that have surfaces that form images through specular reflection. Light rays that strikes the mirror's surface, incident rays, bounce off and become reflected rays. The angle between the incident ray and the mirror's normal (perpindicular) is equal to the angle between the reflected ray and the mirror's normal. This is the law of reflection. Mirrors can produce two types of images: real and virtual. Real images are representations of objects formed by light rays intersecting at a focal point in front of the mirror. Virtual images diverge from a point behind the mirror, where the image appears to exist. Light rays do not actually pass through virtual images. Plane mirrors mirrors always form virtual images. For curved mirrors, however, we must take more certain factors into consideration. Concave Mirrors Concave mirrors are curved mirrors that reflect on the inner surface. In other words, the mirror curves toward the object. In the diagram to the right, C denotes the center of curvature. F denotes the focal point, the point at which light rays striking the mirror converge. F is always halfway between C and A, the point at which the mirror's surface where the principal axis meet. If an object is between A and F, the image will be virtual, positively magnified, and upright. A positively magnified image has a greater height than its source. An upright image exists on the same side of the principal axis as the object. If the object is between F and C, the image will be real, inverted, and positively magnified. If the object exists at C, the image will be real, inverted, but not magnified. If the object rests at more than twice the focal length, the image will be real, inverted, and negatively magnified. |
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| This diagram summarizes many possible scenarios with objects at different locations. The red numbers represent objects and the blue numbers represent the corresponding images. Notice that the object 6 does not produce an image because the object lies directly on the focal point. The image converges at infinity. |
| Convex Mirrors Convex mirrors are curved mirrors that reflect on the outer surface. In other words, the mirror curves away from the object. Convex mirrors have negative focal lengths because F lies on the opposite side of the object. Convex mirrors always produce virtual and real images. Mirror Equations Using the mirror equations, we can calculate the locations of objects, images, and focal points. The above equation is used to determine the magnification, m, of an object once it is reflected. Magnification is positive if the height of the image is greater than the height of the object and vice versa. A positive magnification means that the image is also upright and a negative one means that the image is inverted. The above equation is used to determine the locations of objects, images, and focal lengths. If only given the radius of curvature, divide r by 2 to determine f. The signs of the variable are extremely important because they show direction. f is + if the mirror is concave f is - if the mirror is convex di is + if the image is a real image di is - if the image is virtual hi is + if the image is upright hi is - if the image is real |
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| h = height; i = image; o = object d = distance from mirror; i = image, o = object |
| d = distance from mirror; i = image, o = object f = focal length |
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