Question

The far point of a person suffering from myopia is 2 metres from the eye. Find the focal length and power of the corrective lens that will correct his vision.

• A. $2m,-0.5D$
• B. $2m,+0.5D$
  
• C. $1m,+1D$
  
• D. $2m,-1D$
  

Answer 1

The correct option is A $2m,-0.5D$

The rays coming from any point say O at a distance of 2 m from the eye, are focused on the retina. Parallel rays, after passing through the concave lens, should appear to come from O. By the definition of the focus of a concave lens, the point O is the focus of concave lens used. Hence, focal length should be 2 m.

$p=\frac{1}{f}=\frac{1}{-2}=-0.5D$