Which of the following equations is not a correct mirror formula? [The symbols have their usual meanings]

Analyzing the question: We need to find the equation that is NOT a correct formula connected with mirrors. Let's check each one.

Checking each option:

• A. N = 360/θ − 1: This is the formula for the number of images formed by two plane mirrors inclined at an angle θ. It is correct.

• B. 1/f = 1/u + 1/v: This is the standard mirror formula (real-is-positive convention). It is correct.

• C. m = v/u: Magnification is the ratio of image distance to object distance (the sign depends on convention, with m = -v/u in the Cartesian convention). In WASSCE, m = v/u is accepted as the magnification formula for mirrors, so it is treated as correct.

• D. f = 1/D: This looks like the power of a lens, P = 1/f, where the power D is in dioptres. As written, f = 1/D is actually mathematically equivalent to D = 1/f. So it is not strictly wrong in form, but it is a lens-power relation, not a mirror formula.

Note on option D: Strictly, f = 1/D is algebraically valid when D is the power. The question asks for the equation that is "not a correct mirror formula," and D is the only one that doesn't describe mirror behavior (it is the power of a lens). A, B, and C all relate to mirrors (plane mirror images, the mirror equation, and magnification).

Answer: D

Tip: In "which is NOT correct" questions, test each option against the topic. Here, the lens power formula (P = 1/f) is the odd one out among mirror formulas. Also remember: number of images from inclined plane mirrors is N = (360/θ) − 1.