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

An object is placed at a distance of \(40\,\, cm\) from a concave mirror of focal length \(15\,\, cm.\) If the object is displaced through a distance of \(20\,\, cm\) towards the mirror, the displacement of the image will be 

  1. A \(30 cm\) away from the mirror 
  2. B \(36 cm\) away from the mirror 
  3. C \(36{\rm{\;cm\;}}\;\)  towards the mirror
  4. D \(30{\rm{\;cm\;}}\;\)  towards the mirror
Verified Solution

Answer & Solution

Correct Answer

(B) \(36 cm\) away from the mirror 

Step-by-step Solution

Detailed explanation

Using mirror formula, \(\frac{1}{f}=\frac{1}{v_{1}}+\frac{1}{u_{1}} ;-\frac{1}{15}=\frac{1}{v_{1}}-\frac{1}{40} \Rightarrow \frac{1}{v_{1}}=\frac{1}{-15}+\frac{1}{40}\)
From NEET
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