Question

Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of –50 cm. What is the nature of the lens and its power used by each of them?

NCERT Class X
Science - Exemplar Problems

Chapter_Light – Reflection and Refraction

Answer 1

Power of lens is a kind of ability to light .The unit is Dioptre

Answer 2

$\large\mathrm\purple{Power\:\:of\:\:lens→}$

Degree of convergence and divergence provided by a lens is called the power of the lens. Unit of power of lens is Diopter D. Focal length of the lens used by the first student is in positive hence it is a convex lens. The lens of the second student is a concave lens.

→$\large\bf\pink{p=1/f}$ =1/0.5 =2

→Power of lens (first student) =+2

→Power of lens (second student) = 0.02