Question

3. The focal length of a convex lens is equal to
a. The distance between focus and pole of the convex lens
b. The distance between the focus and twice of focus
C. The distance between the focus and the optical center of the convex lens
d. The distance between optical center and twice of focus.
​

Answer 1

The answer is (c) i.e The distance between the focus and the optical center of the convex lens.

Following is the explanation:

1. Principal Axis of the convex lens: It is the straight line passing through the Center of curvature and the optical center of the Lens.

2. Optical center of the convex lens: It is the point on the principal axis of the lens through which rays of light passes without deflection.

3. Focus of the convex lens: It is the point on the principal axis of the lens where rays of light coming parallel to principal axis after refraction through the lens.