Question

A point on a thin lens, through which light ray passes without any deviation is called ______________.

• A. centre of curvature
• B. optical centre
• C. focus
• D. second focus

Answer 1

The correct option is B

optical centre

Central part of a lens act as a rectangular glass slab, as the curvature of this part of the lens is very small. If the lens is very thin, then the width of the slab will be very small. Also we know that if light falls on a thin rectangular glass slab, then the ray passes almost without deviation. So, for a thin lens if the light goes through the centre of the lens (called optical centre), then it will pass without any deviation.