A coin lies at the bottom of a water tank (\( n = 1.33 \)) with a depth of \( 13.3 \, \text{cm} \). What is its apparent
**Refractive index** n = c/v, water 1.33 means light 1.33 times slower than vacuum. Passing from water to air at 49°, n₁ sinθ₁ =1.33×sin49°≈1.33×0.755=1.004>1, so sinθ₂>1 impossible, total internal reflection occurs, no refraction. Apparent depth = (real depth/n) . Real depth = 13.3 cm , n = 1.33 . Apparent depth = (13.3/1.33) = 10 cm . Substituting values gives 10 cm, which matches expected image position and magnification from mirror/lens formula 1/f = 1/v - 1/u (lens) or 1/f = 1/v + 1/u (mirror), confirming sign conventions and refraction principles.
Ref: NCERT > Physics Book > Ray Optics > Refraction at Plane Surfaces and Snell's Law
