Q133 / 200 · NEET 2006 · Physics

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

  • Correct answer
    A
    zero
  • B
    25
  • C
    50
  • D
    infinite

Solution

Focal length of lens $$ f_1=25 \mathrm{~cm} $$ focal length of concave lens $$ f_2=25 \mathrm{~cm} $$ Power of combination in dioptres $$ \begin{aligned} P=P_1+P_2 & =\frac{100}{f_1}+\frac{100}{f_2} \\ & =\frac{100}{25}+\frac{100}{-25}=0 . \end{aligned} $$

Hence, the correct answer is option: 'A'.

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