Question

what is meant by the power of lens is +1d

Answer 1

Hi there!

1 dioptre is the power of a lens whose focal length is 1 metre.

$1 D$ = $1/m^1$

Note that,
The power of a Convex lens is Positive(+) and that of a Concave lens is Negative (-).

Cheers!

Answer 2

the value 1 shows that the height of the object and image are same the (+) sign shows that the image is virtual