Electron Drift Speed in Copper Wire · CAP 2016 #Q7
Physics · electromagnetism
Problem
Which value is closest to the average net speed of electrons ("drift speed") in a copper wire of radius 1 mm for a current of 3 Amperes? The density of copper at room temperature is about 9 g/cm³ and its molar mass is 63.5 g/mol. a) 6×10⁻⁵ m/s b) 2×10⁻³ m/s c) 3×10⁸ m/s d) 5×10⁰ m/s e) 8×10⁴ m/sIntuitive explanation
Drift speed connects macroscopic current to microscopic electron motion through the relationship , where is the number density of free electrons, is the wire's cross-section, and is drift speed. You'll need to find how many free electrons per unit volume copper has using its density and molar mass, then solve for the surprisingly slow speed at which electrons actually move through the wire despite rapid current flow.
Intuitive explanation
Drift speed connects macroscopic current to microscopic electron motion through the relationship , where is the number density of free electrons, is the wire's cross-section, and is drift speed. You'll need to find how many free electrons per unit volume copper has using its density and molar mass, then solve for the surprisingly slow speed at which electrons actually move through the wire despite rapid current flow.