Apparent Depth Formula — the NEET Physics formula with its derivation, variables, validity constraints and worked solver.
Apparent Depth Formula Refraction at a plane interface when viewed from a rarer medium at near-normal incidence. Apply Snell's Law at the boundary: n1 sin(i) = n2 sin(r) Use paraxial approximation: sin(theta) is approximately tan(theta) Express tan(i) and tan(r) in terms of depth and lateral distance from the normal Substitute and simplify to find n = Real Depth / Apparent Depth Rays must be paraxial (small angles of incidence) Observer is in the rarer medium (usually air) Interface must be flat The formula n = Real/Apparent is only valid when light travels from denser to rarer; if viewed from denser to rarer, the object appears farther away Assuming the depth stays the same regardless of the angle of observation (depth actually depends on the angle of view)