Solve this :
4. An object is placed at a distance of 50 cm from a concave lens of focal length 20 cm. Find the nature and position of the image.

5. An object placed 50 cm from a lens produces a virtual image at a distance of 10 cm in front of the lens. Draw a diagram to show a formation of image. Calculate focal length of lens and magnification produced.

6. The magnification produced by a spherical lens is + 0.75.What is the -
a)  Nature of image.
b) Nature of lens