Problem Two identical charges qqq, placed 1 m1\ \text{m}1 m apart, repel each other with a force of 1,0 N1{,}0\ \text{N}1,0 N. Calculate the value of qqq. Solution Symbolic setup. Equal charges: q1=q2=qq_1 = q_2 = qq1=q2=q. Coulomb’s law gives: F=k q2r2 ⟹ q=F r2kF = k\,\frac{q^2}{r^2} \;\Longrightarrow\; q = \sqrt{\frac{F\,r^2}{k}}F=kr2q2⟹q=kFr2 Numerical substitution. With F=1,0 NF = 1{,}0\ \text{N}F=1,0 N, r=1 mr = 1\ \text{m}r=1 m, k=8,99⋅109k = 8{,}99\cdot 10^9k=8,99⋅109: q=1,0⋅128,99⋅109=1,112⋅10−10=1,055⋅10−5 Cq = \sqrt{\frac{1{,}0\cdot 1^2}{8{,}99\cdot 10^9}} = \sqrt{1{,}112\cdot 10^{-10}} = 1{,}055\cdot 10^{-5}\ \text{C}q=8,99⋅1091,0⋅12=1,112⋅10−10=1,055⋅10−5 C q≈10,5 μC\ev{q \approx 10{,}5\ \mu\text{C}}q≈10,5 μC Links Topics: Electrostatics Concepts: Coulomb’s law Skills: Symbolic setup