Question

Figure shows a convex lens of focal length 15 cm. A point object is placed on the principle axis of lens at a distance 20 cm from it as shown. On the other side of lens two observer eyes O₁ and O₂ are situated at a distance 100 cm from the lens at some distance above and below the principal axis.

Activity I: Now half position of lens below principal axis is painted black. 

Activity II: After this, lens is cut along its horizontal diameter and upper part of it is raised up slightly in vertical direction.

After activity ­ I, for which observer the intensity of image will be reduced to half.

(a)  For O₁

(b)  For O₂

(c)  Both for O₁ and O₂

(d)  Neither for O₁ nor for O₂

Answer 1

Correct option (4) Neither for O₁ nor for O₂

Explanation :

Since one observes sees image due to half portion of lens only, So on covering one half it intensity remains unaffected.