Question

Two identical charges $ q $ are placed 1 m apart. The electrostatic force between them is $ 9 \times 10^{-9} \, \text{N} $. What is the magnitude of each charge? (Take $ k = 9 \times 10^9 \, \text{Nm}^2/\text{C}^2 $)

• A. \( 1 \times 10^{-9} \, \text{C} \)
• B. \( 3 \times 10^{-9} \, \text{C} \)
• C. \( 1 \times 10^{-9} \, \text{C} \)
• D. \( 3 \times 10^{-9} \, \text{C} \)

Hint:

To find the magnitude of identical charges when the force and separation are known, use Coulomb’s law: \[ F = \frac{k q^2}{r^2} \Rightarrow q = \sqrt{\frac{F r^2}{k}} \] Always isolate \( q^2 \) and then take the square root.