Human Eye And The Colourful World Question 15

Question: Q. 3. A student needs spectacles of power - 0.5 D for the correction of his vision.

(i) Name the defect in vision the student is suffering from. (ii) Find the nature and focal length of the corrective lens.

(iii) List two causes of this defect.

A [CBSE Outside Delhi, Set- III, 2019]

Show Answer

Solution:

(i) Myopia

1

(ii) Concave / diverging lens and focal 1/2

Length =200 cm

(iii) (a) Excessive curvature of the eye lens

(b) Elongation of eye ball

[CBSE Marking Scheme, 2019] 1⁄22

Detailed Answer:

(i) Negative power shows that lens is concave, so the student is suffering from myopia/near- sightedness.

(ii) The nature of lens used to correct this defect is concave lens.

Focal length, f=1p1

(iii) Causes of defect are: (0.5)=2 m

=p1(0.5)=2 m

(a) Excessive curvature of the eye lens.

(b) Elongation of the eyeball.



Table of Contents