Question

What is meant by the optical center of a lens?

Hint:

It is the point on the principal axis through which a ray passes without any deviation.

Answer 1

Step 1: Definition.
The optical center of a lens is a fixed point on the principal axis of the lens through which any ray of light passes undeviated (without changing its direction).

Step 2: Explanation.
A ray directed toward the optical center enters and leaves the lens along parallel faces near the center, so it travels straight through and emerges without bending (there is only a negligible lateral shift). The optical center is usually the geometric center of a thin lens.

Step 3: Key property.
Because a ray through the optical center is undeviated, it is used as one of the standard construction rays when drawing ray diagrams for image formation by lenses.

\[\boxed{\text{Point on the axis through which a ray passes undeviated}}\]