JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments
An object is at a distance of \(20\,m\) from a convex lens of focal length \(0.3\,m.\) The lens forms an image of the object. If the object moves away from the lens at a speed of \(5\,m/s,\) the speed and direction of the image will be
- A \(2.26\times 10^{-3}\,m/s\) away from the lens
- B \(0.92\times 10^{-3}\,m/s\) away from the lens
- C \(3.22\times 10^{-3}\,m/s\) towards the lens
- D \(1.16\times 10^{-3}\,m/s\) towards the lens
Answer & Solution
Correct Answer
(D) \(1.16\times 10^{-3}\,m/s\) towards the lens
Step-by-step Solution
Detailed explanation
\(\frac{1}{V}-\frac{1}{-20}=\frac{1}{30}\) \( \Rightarrow \frac{1}{V} = \frac{1}{{0.30}} - \frac{1}{{20}} = \) \( + \frac{{200 - 3}}{{60}} = \frac{{197}}{{60}}\) \( \Rightarrow \quad - \frac{{dV}}{{dt\,\,{V^2}}} + \frac{{du}}{{dt\,{u^2}}} = 0\)…
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