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

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsRay Optics and Optical Instruments1 Mark
MCQ
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.
Assertion: Goggles have zero power.
Reason: Radius of curvature of both sides of lens is same.
  • ✓
    Both $A$ and $R$ are true and $R$ is the correct explanation of $A.$
  • B
    Both $A$ and $R$ are true but $R$ is not the correct explanation of $A.$
  • C
    $A$ is true but $R$ is false.
  • D
    $A$ is false and $R$ is also false.
✓

Answer

Correct option: A.
Both $A$ and $R$ are true and $R$ is the correct explanation of $A.$
Goggles have zero power.
The focal length is given by $\frac{1}{\text{f}}=(\mu-1)\Big(\frac{1}{\text{R}_1}-\frac{1}{\text{R}_2}\Big).$
For goggle lenses, both sides are curved the same way. $R_1$ and $R_2$ are positive.
If they are the same, $\frac{1}{\text{f}}=0$
i.e., power is zero.

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