Question

Define Focal length​

Answer 1

Answer:

here is ur definition of focal length

the focal length is the distance from the optical center of the lens to the imaging sensor when the lens if focused at infinity.

Answer 2

Answer:

for a thin lens in air focal length in the distance from centre of lens to the principal foci or focal point of the lens for example convex lens. the focal length is positive is the distance at which a beam collimated light will be focused to a single spot.