Three light rays parallel and close to the principal axis are incident on a convex lens. At which point will these rays converge after passing through the lens?

Correct option is C

The correct answer is (C) At the focus of the lens

Explanation:
• A convex lens is a converging lens. When light rays that are parallel to its principal axis pass through it, the lens refracts them inward.
• Due to the geometry and varying thickness of the lens (thicker in the middle, thinner at the edges), all paraxial rays (rays parallel and close to the principal axis) intersect at a single distinct point on the principal axis on the other side of the lens.
• This specific point of convergence is fundamentally defined as the principal focus (F) of the convex lens.

Information Booster:
• Focal Length: The distance between the optical center of the lens and the principal focus is called the focal length.
• Real Image: Since the light rays actually meet at the focus, a convex lens can form a real and inverted image that can be captured on a screen.
• Burning Glass: This converging property is why a convex lens can be used to start a fire by focusing the sun's parallel rays to a single intense hot spot.

Additional Knowledge:
• Option A & D: Light rays specifically parallel to the principal axis do not arbitrarily converge at "any point." They are precisely directed to the focal point by the laws of refraction.
• Option B (Optical center): The optical center is the exact middle point of the lens. A ray of light passing through the optical center goes straight through without any deviation, but parallel rays do not converge there.