Key Concepts: Lenses & Mirrors

Mirrors

• Concave mirror: Converging — forms real (inverted) or virtual (upright, magnified) images.
• Convex mirror: Diverging — always forms virtual, upright, diminished images.
• Mirror equation: 1/f = 1/d_o + 1/d_i.

Lenses

• Convex (converging) lens: Positive focal length. Can form real or virtual images.
• Concave (diverging) lens: Negative focal length. Always forms virtual, upright, diminished images.
• Thin lens equation: 1/f = 1/d_o + 1/d_i (same form as mirror equation).

Magnification

• m = −d_i/d_o = h_i/h_o.
• |m| > 1: enlarged. |m| < 1: diminished. Negative m: inverted.