Question

the near point of a hypermetropic person is 75 cm calculate the focal length and power of the lens used in his spectacles

Answer 1

Hello mate

here is your answer

Given,

v = - 75 cm,
u = - 25 cm

From the formula of lens:

=> 1/F = 1/V-1/U

=> 1/F = 1/-75-(-1/25)

=> 1/F = -1/75+1/25

=> 1/F = -1/75+3/75

=>1/F = 2/75

=> F = 37.5 cm

Means,

F= 37.5 cm

from power of lens formula

=> P=1/F in mere

=> P = 1/37.5/100

=> P = 1000/ 375

=> P= +2.66D

The corrective lens needs to have a converging power of +2/66 or +2.67 dioptres, i.e., convex lens.
 
I hope helps you