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 35
Fig. 3,792.—Virtual focus in double concave lens. CASE I: Parallel incident rays. Fig. 3,793.—Virtual focus in double concave lens. CASE II: Divergent incident rays. In thiscase where the rays radiate from a point L on the axis, it is found by the same constructionthat a virtual focus is formed at…
Electrical engineering
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