$A$ girl was playing with a thin beam of light from her laser torch by directing it from different directions on a convex lens held vertically. She was surprised to see that in a particular direction the beam of light continues to move along the same direction after passing through the lens. State the reason for this observation.

(N/A) The beam of light must be passing through the optical centre of the lens.
When a light ray passes through the optical centre of a lens,it does not undergo any refraction or deviation.
This is because the central part of the lens acts like a very thin glass slab,allowing the light to pass straight through without changing its path.