Practice question

**Lens maker's formula** 1/f = (n-1)(1/R₁ - 1/R₂), n refractive index, R₁,R₂ radii of curvature (m), sign convention R positive if surface convex towards incident light. For double convex R₁=12 cm, R₂=-12 cm, n=1.5, 1/f=(0.5)(1/12 -1/(-12))=(0.5)(2/12)=1/12, f=12 cm, converging. In a plane mirror, the reflected rays do not actually converge but appear to diverge from a point behind the mirror when traced backward. This apparent origin of rays behind the mirror results in a virtual image that cannot be projected onto a screen. Substituting values gives Due to apparent divergence from behind the mirror, which matches expected image position and magnification from mirror/lens formula 1/f