Question

The focal length is the distance from the optical center of the lens to its principle__________________
A. Focus.
B. Axis.
C. Center of curvature.
D. Lens.

Answer 1

Hint:Let us learn about what is meant by focal length or distance. It is a distance from the center of the lens to the principal foci of the lens, where parallel rays of light meet or converge. For example, convex lens focal length is negative and distance from the collimated beam seems to radiate through the lens.

Complete answer:
Focal length represents in millimeters, the basic description of focal length is, Longer focal length and Shorter focal length. In Longer focal length, narrower the angle of view and higher magnification. Whereas in Shorter focal length, wider the angle of view and lower magnification.

Now let us know about the optical center of the lens. It is defined as the point which lies on the principal axis through the rays of the light passes without any deflection.

From the top of the diagram we can observe that there is a focal point which emits the light rays to a certain point. From that point the lights emerged in parallel lines passing through the center of the convex lens. Now we can observe that the distance between the focal point and center of the convex lens is called focal length. As we clearly discovered within the diagram. Focal length is the distance from the optical center of the lens to its principal lens.

Hence, the correct answer is option D.

Note: We can simply conclude the gap between focal length and optical center by perceptive the image. In a double convex lens the focal length is greater because it has two curved surfaces, due to the second curved surface. In double convex focal lengths are more preferable.