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in this figure because the source is assumed to be very far from the mirror. We call focal point F and the image distance the focal length f, where (36.5) In Figure 36.8, the colored beams are traveling parallel to the principal axis and the Focal length is a parameter particular to a given mirror and therefore can be used to compare one mirror with another. The mirror equation can be expressed in terms (36.6) Notice that the focal length of a mirror depends only on the curvature of the mirror 1 & 1 q " 1 f " R 2 S E C T I O N 3 6 . 2 • Images Formed by Spherical Mirrors 1133 C F R f (a) Henry Leap and Jim Lehman Figure 36.12 (a) Light rays from a distant object (p : ') reflect from a concave mirror through the focal point F. In this case, the image distance q # R/2 " f, where f is the focal length of the mirror. (b) Reflection of parallel rays from a concave mirror. ▲ PITFALL PREVENTION 36.2 The Focal Point Is Not the Focus Point The focal point is usually not the A satellite-dish antenna is a concave reflector for televi- sion signals from a satellite in orbit around the Earth. The signals are carried by microwaves that, because the satellite is so far away, are parallel when they arrive at the dish. These waves reflect from the dish and are focused on the receiver at the focal point of the dish. Focal length Mirror equation in terms of focal length Courtesy of Thomson Consumer Electronics (b) |