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JEE Mains · Physics · STD 12 - 9. Ray optics and optical instruments

A thin cylindrical rod of length \(10\,cm\) is placed horizontally on the principle axis of a concave mirror of focal length \(20\,cm\). The rod is placed in a such a way that mid point of the rod is at \(40\,cm\) from the pole of mirror. The length of the image formed by the mirror will be \(\frac{x}{3} cm\). The value of \(x\) is \(............\).

  1. A \(30\)
  2. B \(32\)
  3. C \(31\)
  4. D \(59\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(32\)

Step-by-step Solution

Detailed explanation

\(U_A=-45\,cm , f =-20\,cm\) \(V_A=\frac{-45 \times(-20)}{-45-(-20)}=\frac{-900}{25}=-36\,cm\) \(\text { And } U_B=-35\,cm\) \(\therefore V_B=\frac{-35 \times(-20)}{-35-(-20)}=\frac{700}{-15}\) \(\therefore V_A-V_B=\text { length of image }\)…
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