Question

What is meant by power of lens? What does its sign(positive or negative) indicate?

Answer 1

The power of a lens is the measure of its ability to converge or diverge a parallel beam of light on refraction through it .Negative sign for Concave lens and Positive sign for Convex lens. The S.I.unit of power is dioptre (D).
 
       when           f = 1m
​                          P = 1/1m  = 1m-1 = 1dioptre (D)
                     
                           P=1/f (in  m)  =100/ f(in  cm)

Answer 2

The power of a lens is the measure of its ability to converge or diverge a parallel beam of light on refraction through it .

Negative sign for Concave lens and Positive sign for Convex lens. The S.I.unit of power is dioptre (D).

 

      when           f = 1m

​                          P = 1/1m  = 1m-1 = 1dioptre (D)