Drive an expression for equivalent focal length of two thin lenses kept in contact.
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Β Let theΒ focal lengths of the two lenses be f1β and f2β. u1β=OC1β and Β v1β=I1βC1β u2β=βC1βI1β which is approximately equal to C2βI1β Β Β and v2β=C2βI which is approximately equal to C1βI β΄u1β1β+v1β1β=f1β1β and u2β1β+v2β1β=f2β1β OC1β1β+I1βC1β1β=f11β and βC1βI1β1β+C1βI1β=f2β1β So OC1β1β+I1βC1β1β=f1β1β+f2β1β=F1β. Combined focal length of two thin lenses in contact is given by: F=f1β+f2βf1βf2ββ
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