The field of view of a convex mirror is wider than that of concave mirror and convex mirror always produces erect image of object, so we prefer convex mirror as rear view mirror for vehicles.

\(\therefore\) Focal length, \(f=\frac{1}{Power}=\frac{1}{(-2)}=-0.5 \quad m\)
Since, f is negative, lens is concave.

The rough focal length of a convex lens is obtained by forming sharp image of a very distant object on a screen. The distance of the screen from the lens gives us the rough focal length of the lens.
This method is not applicable to a concave lens, as image formed by a concave lens is virtual and it cannot be taken on the screen.

The focal length of a lens depends on
(a) Radii of curvature of the surface of the lens.
(b) Nature of material of the lens.
(c) Nature of medium in which lens is placed.

No, This method is not applicable to a concave lens, as image formed by a concave lens is virtual and it cannot be taken on the screen.