Worked example: A plastic rod is rubbed with fur and gains a net charge of −3.2 × 10⁻⁹ C. How many excess electrons does it carry, and could it instead carry −3.0 × 10⁻¹⁹ C? Step 1: Each electron carries −e = −1.602 × 10⁻¹⁹ C. Number of excess electrons n = Q/e = (3.2 × 10⁻⁹)/(1.602 × 10⁻¹⁹) ≈ 2.0 × 10⁷ electrons. Step 2: −3.0 × 10⁻¹⁹ C is not an integer multiple of e (3.0/1.602 ≈ 1.87, not a whole number), so by quantization it is impossible — any real charge must equal ±ne exactly. Step 3: Note the rod gained electrons (negative charge), so the fur lost them and became equally positive — charge conserved overall.