Question

Two lenses have power(i)+2 dioptre,(ii)-4 dioptre.What is the nature and focal length of each lens

Answer 1

(i)p=1/f

   2=1/f

f=1/2=0.5(converging lens)

(ii) -4=1/f

f=1/-4= -1/4=0.25

Answer 2

(A)Power of a lens= 1/focal length-------------- f=1/2=0.5. As the power is given in +ve sign, it is a concex lens--------------------(b) p=1/f------------- f=1/4= 0.25. -- as the power is in -ve , it is a concave lens