image

Meaning: A mirror or lens redirects rays from each point on an object. If the rays actually converge at a point, the image is real: it can be projected on a screen and, for a single mirror or lens, is inverted. If the rays only appear to diverge from a point when traced backward, the image is virtual: it is upright for a single mirror or lens and cannot be projected.

Equation: 1/f = 1/o + 1/i and m = −i/o = hi/ho, where f is focal length (m), o is object distance (m), i is image distance (m), m is magnification (unitless), and hi and ho are image and object heights (m). Positive i means real; negative i means virtual. f is positive for converging mirrors and lenses and negative for diverging ones.

On the MCAT: You are given f and o, solve for i and m, then describe the image as real or virtual, upright or inverted, enlarged or reduced. A converging lens with the object beyond f gives a real, inverted image; with the object inside f it gives a virtual, upright, enlarged image (a magnifying glass). A plane mirror gives a virtual, upright image with i = −o and m = +1.

Common confusion: Virtual does not mean unseen; the eye sees virtual images fine. Real versus virtual depends only on whether rays truly converge, not on size. The sign of i (real or virtual) and the sign of m (inverted if negative) are separate checks.