WBJEE · Physics · Ray Optics
An object placed at a distance of \(16 \mathrm{cm}\) from a \(\begin{array}{llll}\text { convex lens } & \text { produces } & \text { an image } & \text { of }\end{array}\) magnification \(m(m>1)\). If the object is moved towards the lens by \(8 \mathrm{cm}\), then again an image of magnification \(m\) is obtained. The numerical value of the focal length of the lens is
- A \(12 \mathrm{cm}\)
- B \(14 \mathrm{cm}\)
- C \(18 \mathrm{cm}\)
- D \(20 \mathrm{cm}\)
Answer & Solution
Correct Answer
(A) \(12 \mathrm{cm}\)
Step-by-step Solution
Detailed explanation
Linear magnification, \(m=\frac{f}{f+u}\) As given that magnification is same for both cases this is possible if the two different values of \(u\) are of opposite sign. \(i, \theta,+\frac{f}{f-16}=\frac{-f}{f-8}\) \(\Rightarrow \quad 16-f=f-8\) \(\Rightarrow \quad 2 f=24\) or…
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