Hawkins electrical guide ... : questions, answers & illustrations : a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications ; a practical treatise (1914)
Hawkins, N. (Nehemiah), 1833-1928 · New York : T. Audel & Co. · leaf 32
nvex lenses have both real and virtual foci, like concave mirrors. 2,686 HAWKINS ELECTRICITY Principal Foci.—Fig. 3,786 shows the case in which the luminousrays which fall on the lens are parallel to its principal axis. In the figure^ any incident ray as LB, in approaching the normal ofthe point of… … M Fig. 3,786.—Principal focus in double convex lens.parallel to the principal axis. CASE I: Rays jrom luminous source
Electrical engineering
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