Question

Two point charges 5μC and 4μC are 10 cm apart. Find the force by which they will repel each other.
1. 10 N
2. 36 N
3. 18 N
4. 9 N

Answer 1

Correct Answer - Option 3 : 18 N

CONCEPT:

• Coulomb’s law is an inverse square law of force that describes the electrostatic force between charged particles.
• Electrostatic Force: between two charges q1 and q2 at the distance of R is given by:

\(F=\frac{1}{4\pi ϵ_0}\frac{q_1q_2}{R^2} \)

where F is the electrostatic force, q1 and q2 are the charges, and ϵ0 is the electrical permittivity of the vacuum.

CALCULATION:

Given that q₁ = 5μC and q₂ = 4μC R = 10cm = 0.1m;

We know \(F=\frac{1}{4\pi ϵ_0}\frac{q_1q_2}{R^2} \)

\(F=9×10^9×\frac{5μC \times 4μC}{0.1^2} \)

\(F=9×10^9×\frac{5​​​​ \times 10^{-6} \times 4 \times 10^{-6}}{0.1^2} =18\)

F = 18 N

So the correct answer is option 3.