COMEDK · Physics · 25. Ray Optics
A concave mirror gives an image three times as large as its object placed at a distance of \(20 \mathrm{~cm}\) from it. For the image to be real, the focal length should be
- A \(10 \mathrm{~cm}\)
- B \(15 \mathrm{~cm}\)
- C \(20 \mathrm{~cm}\)
- D \(30 \mathrm{~cm}\)
Answer & Solution
Correct Answer
(B) \(15 \mathrm{~cm}\)
Step-by-step Solution
Detailed explanation
Given, size of image formed by concave mirror, \[ h_{2}=3 h_{1} \] where, \(h_{1}\) is the size of object. \[ m=\frac{h_{2}}{h_{1}}=\frac{3 h_{1}}{h_{1}}=3 \] But for real image, magnification \(m\) will be negative. \(\therefore \quad m=-3\) \(\Rightarrow \quad-\frac{v}{u}=-3\)…
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