Question

Distinguish between:
a. Farsightedness and Nearsightedness
b. Concave lens and Convex lens

Answer 1

a.

Farsightedness	Nearsightedness
In this defect, person clearly sees all the far away objects, but is unable to see the nearby objects comfortably and clearly.	In this defect, person clearly sees all the nearby objects, but is unable to see the distant objects comfortably and clearly.
It is caused due to decrease in curvature of eye lens or decrease in length of eyeball.	It is caused due to increase in curvature of eye lens or increase in length of eyeball.
In this defect, image is formed behind the retina.	In this defect, image is formed in front of the retina.
It is corrected using convex lens.	It is corrected using concave lens.

b.

Concave lens	Convex lens
It is a diverging lens because it diverges the rays falling on it.	It is a converging lens because it converges the rays falling on it.
It is thin at the center and bulged at the edge.	It is thin at the edge and bulged at the centre.
The image formed by concave lens is always diminished and virtual.	The image formed by convex lens can be real as well as virtual. Also, the image formed can be diminished as well as magnified.
It has a virtual focus.	It has a real focus.