# . One half of a convex lens of focal length 10 cm is covered with a black paper

Can such a lens produce an image of a complete object placed at a distance of 30 cm from the lens? Draw a ray diagram to justify your answer

A 4 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 15 cm. Find nature, position and size of the image.

Ans. (i) Yes. If a convex lens of focal length 10 cm is covered one half with a  black paper, it can  produce   an  image  of  the  complete object between  F2  and  2F2.  The rays of Object 2 F1 light coming from the object get refracted by the upper half of the lens. The image formed will be real inverted and diminished.

(ii) Object height, h1 = 4 cm

Focal length, f = +20 cm

Image distance, v = ?

Object distance, u= -15 cm

Image height, h2 =?

By lens formula,

Negative sign of h2 shows that the image is erect.

Therefore, a virtual, erect, magnified (16 cm) image will be formed at a distance of 60 cm on the same side as of the object by the convex lens.