A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in diopters of the combination is

25

50

infinite

zero

Solution

zero

Focal length of combination of lenses placed in contact is
$1 over straight F space equals space 1 over straight f subscript 1 space plus space 1 over straight f subscript 2$
For convex lens,    $straight f subscript 1 space equals space 25 space cm$
For concave lens, $straight f subscript 2 space equals space minus 25 space cm$
Hence,    $1 over straight F space equals space 1 over 25 plus fraction numerator 1 over denominator negative 25 end fraction$
   $equals 1 over 25 minus 1 over 25 space equals space 0$
$therefore$ $straight F space equals space 1 over 0 space equals space infinity$
Hence, power of combination
   $straight P space equals space 1 over straight F space equals space 0 space straight D$

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Wave Optics

A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in diopters of the combination is

25

50

infinite

zero

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Wave Optics

A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in diopters of the combination is 25 50 infinite zero

Some More Questions From Wave Optics Chapter

Mock Test Series

NCERT Sample Papers

Entrance Exams Preparation

A convex lens and a concave lens, each having same focal length of 25 cm, are put in contact to form a combination of lenses. The power in diopters of the combination is

25

50

infinite

zero