Practice question

**Two lenses in contact** behave as single lens with power sum, magnification product m = m₁×m₂. For f₁=20 cm (P₁=5 D), f₂=-20 cm (P₂=-5 D) in contact, P=0, F infinite, afocal system, beam emerges parallel, principle of corrective lenses for myopia/hypermetropia. Objective magnification: m_o = (L/f_o) . L = 20 cm , f_o = 2 cm ⇒ m_o = (20/2) = 10 . Eyepiece magnification: m_e = 5 (given). Total magnification: m = m_o × m_e = 10 × 5 = 50 . Substituting values gives 50, which matches expected image position and magnification from mirror/lens formula 1/f = 1/v - 1/u (lens) or 1/f