What is an image?

If the focal length of the objective lens is increased,then the magnifying power of:

Two blocks each of mass $m$ lie on a smooth table. They are attached to two other masses as shown in the figure. The pulleys and strings are light. An object $O$ is kept at rest on the table. The sides $AB$ and $CD$ of the two blocks are made reflecting. The acceleration of the two images formed in those two reflecting surfaces with respect to each other is:

What is an image? Explain its types.

If the luminous efficiency of a lamp is $2 \text{ lumen/watt}$ and its luminous intensity is $42 \text{ candela}$,then the power of the lamp is.......$W$

$A$ finite size object is placed normal to the principal axis at a distance of $30 \ cm$ from a convex mirror of focal length $30 \ cm$. $A$ plane mirror is now placed in such a way that the image produced by both the mirrors coincide with each other. The distance between the two mirrors is (in $cm$)