Two lenses of focal lengths f1 and f2 are kept in contact coaxially. The resultant power of combination will be
A. \(\frac { { f }_{ 1 }{ f }_{ 2 } }{ { { f }_{ 1 }-f }_{ 2 } } \)
B. \(\frac { { f }_{ 1 }{ +f }_{ 2 } }{ { { f }_{ 1 }f }_{ 2 } } \)
C. \({ f }_{ 1 }{ +f }_{ 2 }\)
D. \(\frac { { f }_{ 1 } }{ { f }_{ 2 } } +\frac { { f }_{ 2 } }{ { f }_{ 1 } } \)
Answer:B
Two lenses of focal lengths f1 and f2 are kept in contact coaxially. The resultant power of combination will be
A. \(\frac { { f }_{ 1 }{ f }_{ 2 } }{ { { f }_{ 1 }-f }_{ 2 } } \) B. \(\frac { { f }_{ 1 }{ +f }_{ 2 } }{ { { f }_{ 1 }f }_{ 2 } } \) C. \({ f }_{ 1 }{ +f }_{ 2 }\) D. \(\frac { { f }_{ 1 } }{ { f }_{ 2 } } +\frac { { f }_{ 2 } }{ { f }_{ 1 } } \)