question_answer

Two thin lenses of focal lengths f1 and f2 are in contact.  The focal length of this combination is   [MP PET 2002]

A)            \[\frac{{{f}_{1}}{{f}_{2}}}{{{f}_{1}}-{{f}_{2}}}\]          

B)            \[\frac{{{f}_{1}}{{f}_{2}}}{{{f}_{1}}+{{f}_{2}}}\]

C)            \[\frac{2{{f}_{1}}{{f}_{2}}}{{{f}_{1}}-{{f}_{2}}}\]       

D)            \[\frac{2{{f}_{1}}{{f}_{2}}}{{{f}_{1}}+{{f}_{2}}}\]