The magnitude of the electric field produced by a single point charge q at distance r is:

• A. E = k q / r^2
• B. E = k q / r
• C. E = k q r^2
• D. E = k q r

Answer: (A)

Electric fields from a point charge follow an inverse-square law: the field strength weakens with the square of the distance. If a small test charge is placed at distance r, the force it experiences is F = k q q0 / r^2. By definition, the electric field is F divided by the test charge q0, so E = F / q0 = k q / r^2. Taking magnitude gives E = k |q| / r^2. The field points radially: away from the charge if q is positive and toward it if q is negative. This 1/r^2 dependence is what sets the correct form apart from the other options.