Question

Assertion: A lens with a focal length of 50 cm has a power of 2 dioptres.

Reason: The power of a lens is the reciprocal of its focal length in metres.

\[ \text { Power }=\frac{1}{\text { Focal length }(\mathrm{m})}\]

Options

• If both Assertion and Reason are true and the Reason is correct explanation of the Assertion.

• If both Assertion and Reason are true, but Reason is not correct explanation of the Assertion.

• If Assertion is true, but the Reason is false.

• If Assertion is false, but the Reason is true.

Answer 1

If both Assertion and Reason are true and the Reason is correct explanation of the Assertion. 

Explanation:

Using the definition of lens power $$P = \frac{1}{f\text{ (m)}} = \frac{1}{0.50\text{ m}} = 2\text{ dioptres}$$, the assertion is completely verified and explained by the reason.