Question

21. 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 form 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 lend of focal length 20 cm. The
distance of the object from the lens in 15 cm. Find the nature, position and size of the image.
OR​

Answer 1

Answer:

To observe a convex lens which can produce the complete image of the object whereas half of the lens is covered. Because light coming from the object can be refracted from the other half of the lens. Therefore, the intensity of light will be reduced.

Object size  h=+4cm

Object distance u=–20cm

Focal length f=–10cm

Image distance v=?

Image size h′ =?

we know,

1/f = 1/u + 1/v

1/v = 1/f - 1/u

1/v = -1/20

v=−20

The screen should be placed at 20 cm from the mirror. The image is real.

Also magnification m=-1

So, the image is inverted and enlarged.