Question

Q1.Define lateral magnification.

Q2. A concave mirror and a concave lens are held in water. What changes, if any, do you expect in their focal length?

Answer 1

1.the ratio of the height of the image to the height of the object in a lensor other optical system.
2.Focal length of any mirror (concave) does not depend on medium, so it remains unchanged. 
If refractive index of the material of convex lens is greater than that of water, then its focal length will increase. 
If refractive index of the material of convex lens is equal to that of water, then its focal length will become infinity. 
If refractive index of the material of convex lens is less than that of water, then its focal length will become negative i.e it will behave like concave lens.