Question

Aniket from Std. X uses spectacles. The power of the lenses in his spectacles is - 0.5 dioptre.
Answer the following questions:

1. State the type of lenses used in his spectacles.
2. Name the defect of vision Aniket is suffering from.
3. Find the focal length of the lenses used in his spectacles.

Answer 1

1. Concave :
   Concave since the power of the lens is negative.
    
   
   
2. Aniket suffers from an eye defect known as myopia.
3. Power of lens in dioptre  = `1/"focal length in metres"`.
   
   
   Therefore,  - 0.5 = `1/"f(m)"`
   
   
   Therefore, f(m) = `1/- 0.5`
   
   
   Therefore, f(m) = 2m.
   
   
   Therefore, the focal length of the lenses used in Aniket’s spectacles is - 2 m.