question_answer

Assertion             :       Although the surfaces of a goggle lens are curved, it does not have any power. Reason                 :   In case of goggles, both the curved surfaces have equal radii of curvature.

A)             If both assertion and reason are true and the reason is the correct explanation of the assertion.

B)             If both assertion and reason are true but reason is not the correct explanation of the assertion.

C)             If assertion is true but reason is false.

D)             If the assertion and reason both are false.

E)             If assertion is false but reason is true.

Correct Answer: A

Solution :

                   The focal length of a lens is given by \[\frac{1}{f}=(\mu -1)\,\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)\] For, goggle, R­1 = R2                                        \ \[\frac{1}{f}=(\mu -1)\,\left( \frac{1}{{{R}_{1}}}-\frac{1}{{{R}_{2}}} \right)=0\]. Therefore, \[P=\frac{1}{f}=0\]