RRB Group D 27 Nov 2025 Shift 2 Solved Paper

Concept:The New Cartesian Sign Convention in optics defines sign rules for distances.It states that the object is always placed to the left of the lens or mirror.This ensures consistent direction of incident light (from left to right).Explanation:According to the convention, the object is placed to the left of the lens.Therefore, the object distance ($u$) is measured from the optical center to the object.Since this measurement is opposite to the direction of incident light, $u$ is taken as negative.Thus, statement A ("object distance is always positive") is false.Statement B ("object is placed to the left of the lens") is correct.Statement C is false because light falls on the lens from the left-hand side, not the right.Statement D is false because the object is assumed to lie on the principal axis, not necessarily above it.The principal axis is the line through the optical center perpendicular to the lens.Distances measured along the direction of incident light are positive; opposite is negative.This convention simplifies calculations using the lens formula: $\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$.For a convex lens, $f$ is positive; for a concave lens, $f$ is negative.Answer:The object is always placed to the left of the lens. Option B is correct.