Practice question

**Lens formula** 1/f = 1/v - 1/u, f focal length (m), u object distance, v image distance, sign: u negative if object left of lens in Cartesian convention, magnification m = v/u, real image inverted m negative, virtual erect m positive. Power P = 1/f (diopters D), f in meters, +5 D means f=0.2 m=20 cm converging. Magnification: m = 1 + (D/f) . D = 25 cm , f = 5 cm . m = 1 + (25/5) = 1 + 5 = 6 . Substituting values gives 6, which matches expected image position and magnification from mirror/lens formula 1/f = 1/v - 1/u