A student repeating Coulomb's experiment made the following observations: Given charges 2.3600 × 10⁻⁸ C and 5.000 × 10⁻¹⁵ and a separation of 1.0057 cm, the electric force between them is 1.00 × 10⁻⁶ N. What value of k does this indicate, and what are two possible reasons the student found a different value from the known constant?