Question

1. Define 1 dioptre of power of a lens.
2. Convert length for my real and inverted needle at a distance of 50 cm from it where is the needle placed in the front of the convex lens if the image is equal size of the object also find the power of lens.
3. Find the power of concave lens of focal length 2 metre​

Answer 1

Answer:

dioptre (British spelling) or diopter (American spelling) is a unit of measurement of the optical power of a lens or curved mirror, which is equal to the reciprocal of the focal length measured in metres. (1 dioptre = 1 m−1.) ... For example, a 3-dioptre lens brings parallel rays of light to focus at 1⁄3 metre.