The correct option is It emerges undeviated.
Explanation
The optical center is a central point on the principal axis of a lens. It is a fundamental reference point used in ray optics to determine the path of light rays and the formation of images by spherical lenses (convex or concave).
Detailed Analysis
- Behavior of Light at the Optical Center: When a ray of light is directed towards the optical center of a thin lens, it passes through the lens without suffering any deviation.
- Physical Reason: At the optical center, the two curved surfaces of the lens are virtually parallel to each other. Consequently, the central portion of the lens acts like a very thin rectangular glass slab.
- Thin Lens Approximation: While a glass slab causes a slight lateral displacement of the incident ray, in a "thin" lens, the thickness is considered negligible. Therefore, the lateral displacement is effectively zero, and the ray emerges in a straight line along its original path.
- Comparison with Other Options:
- It reflects back along the same path describes reflection, which occurs in mirrors, not during transmission through a lens.
- Options It bends towards the principal axis and It bends away from the principal axis describe the bending (refraction) that occurs when light strikes the lens at points other than the optical center, causing convergence or divergence.
Key Takeaway: The defining property of the optical center of a thin lens is that any ray of light passing through it remains undeviated.