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

Bihar 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: Goggles have zero power.
Reason: Radius of curvature of both sides of lens is same.
✓

Answer

  1. Both A and R are true and R is the correct explanation of A.

Explanation:

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. R1 and R2 are positive. If they are the same, $\frac{1}{\text{f}}=0$ i.e., power is zero.

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