. 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.


Best Answer

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.


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