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Ray Optics and Optical Instruments — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsRay Optics and Optical Instruments1 Mark
Question
Two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  1. Both A and R are true and R is the correct explanation of A.
  2. Both A and R are true but R is not the correct explanation of A.
  3. A is true but R is false.
  4. A is false and R is also false.
Assertion: A convex lens of glass $(\mu = 1.5)$ behave as a diverging lens when immersed in carbon disulphide of higher refractive index $(\mu = 1.65).$
Reason: A diverging lens is thinner in the middle and thicker at the edges.
✓

Answer

  1. Both A and R are true but R is not the correct explanation of A.
Explanation:

$\mu=\frac{\mu_\text{g}}{\mu_\text{c}}=\frac{1.5}{1.65}<1$

From $\frac{1}{\text{f}}=(\mu-1)\Big(\frac{1}{\text{R}_1}-\frac{1}{\text{R}_2}\Big)$ f becomes negative.

Therefore, the lens behaves as a diverging lens.

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