(A) (i) The given lens is a convex lens as power of convex lens is positive.
(ii)
P‌=‌

1

f

+2‌=‌

1

f

f‌=+0.50m
Its focal length is +0.50m.
Using the relation ‌

1

f

=‌

1

v

−‌

1

u

‌

1

v

‌=‌

1

f

+‌

1

u

‌=‌

1

0.5

+‌

−1

1

=‌

2+(−1)

1

v‌=1m
OR
OR
(B) (i) Principal focus: Several rays of light parallel to the principal axis are falling on a concave lens. These rays, after refraction from the lens, are appearing to diverge from a point on the principal axis. This point on the principal axis is called the principal focus of the concave lens.
(ii) Focal length: The distance of the principal focus from the optical centre of a lens is called its focal length. The letter f is used to represent the focal length.