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:

Correct answer: A. zero Focal length of lens f_1=25 ~cm focal length of concave lens f_2=25 ~cm Power of combination in dioptres aligned P=P_1+P_2 & =(100)/(f_1)+(100)/(f_2) & =(100)/(25)+(100)/(-25)=0 . aligned

NEET 2006

Exam: NEET
Year: 2006
Subject: Physics
Chapter: Ray Optics

NEET 2006 · Physics · Ray Optics

A convex lens and a concave lens, each having same focal length of...

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:

Options

Azero
B25
C50
Dinfinite

Correct answer

A. zero

Step-by-step 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}

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