Question

The focal length is the distance from the lens (or mirror) to the: image object focal point center of curvature

Answer 1

Answer:

Focal length is the distance of center of the lens from its FOCAL POINT

Explanation:

As we know that when straight beam of light incident on the lens which is parallel to the principle axis of the lens then this light will get refracted by the lens

After the refraction from the lens the light will pass through the a point on the principle axis. That common point is known as FOCAL POINT.

As as per lens formula we know that

$\frac{1}{d_i}{ + \frac{1}{d_o} = \frac{1}{f}$

now we have

$d_o = infinite$

so here we have

$d_i = f$

so focal point will be the point where image formed when straight parallel beam of light passes through it.

Answer 2

The answer is focal point.
The focal length is the distance from the lens (or mirror) to the focal point. The focal point is the point at which rays of light converge.