Cartesian sign conventionकार्तीय चिह्न परिपाटीCartesian sign convention
NCERT Fig 9.2 · Class 12 Physics · Chapter 9 · interactive diagram
Parts and what they mean
- Direction of incident light (आपतित प्रकाश की दिशा) — Draw light coming from the LEFT. This direction is the +x direction.
- Positive distances (धनात्मक दूरियाँ) — Measured from P in the same direction as the incident light: positive.
- Negative distances (ऋणात्मक दूरियाँ) — Measured from P opposite to the incident light: negative. So for a real object in front of a mirror or lens, u is always negative.
- Heights above the axis: + (अक्ष के ऊपर ऊँचाई: +) — Heights measured upward from the principal axis are positive (an erect object).
- Heights below the axis: − (अक्ष के नीचे ऊँचाई: −) — Heights measured downward are negative — an inverted image has h′ < 0.
- Object (वस्तु) — Lies to the left of P, against the incident light: u is negative; h is positive.
- Real image of a concave mirror (अवतल दर्पण का वास्तविक प्रतिबिंब) — Forms in front of the mirror (left of P), so v < 0; it is inverted, so h′ < 0.
- Pole P = origin (ध्रुव P = मूल बिंदु) — Every distance (u, v, f, R) is measured from here.
- Concave mirror (अवतल दर्पण) — A reflecting surface that is part of a hollow sphere, silvered on the outside so it reflects from the inside (curved in towards the object). Converging.
- Principal axis = x-axis (मुख्य अक्ष = x-अक्ष) — Distances are measured along it.
Original diagram drawn by Simple Learning Hub, based on NCERT Fig 9.2. Report a mistake