Electric Field Strength Calculator
Calculate electric field around a point charge and force on test charges using Coulomb's law.
⚡ Physics📐 E = kQ/r²
Source charge Q (Coulombs)
Distance r (meters)
Test charge (Coulombs, optional)
Please enter valid values.
Formula & Reference
| Variable | Formula | Units |
|---|---|---|
| Electric Field Strength Calculator | E = kQ/r² | N/C |
Step-by-Step Examples
Example 1
1 μC at 10cm
Q=1e-6 C, r=0.1 m.
- E = 8.99e9 × 1e-6 / 0.01 = 899,000 N/C
✓ 899,000 N/C
Example 2
Proton at 1nm
Q=1.6e-19 C, r=1e-9 m.
- E = 8.99e9 × 1.6e-19 / (1e-9)² = 1.44×10¹¹ N/C
✓ 1.44×10¹¹ N/C
Example 3
Force on Test Charge
Q=1e-6, r=0.1m, test charge 2e-6 C.
- E=899,000 N/C | F = 899,000 × 2e-6 = 1.798 N
✓ F = 1.798 N
Real-World Applications
Physics Students
Learn Coulomb's law with real charge calculations.
Electrical Engineers
Calculate field strengths near conductors.
Physics Teachers
Demonstrate electrostatic calculations.
Research Physicists
Calculate electrostatic interactions.
Common Mistakes to Avoid
⚠️
Wrong SI units
Charge in Coulombs, distance in meters, force in Newtons. 1 μC = 10⁻⁶ C.
⚠️
E field vs force
E (N/C) is a field property. Force on a test charge F = qE.
Frequently Asked Questions
Coulomb's constant k? ▾
k = 8.99×10⁹ N·m²/C². Electromagnetism is ~10³⁶ times stronger than gravity.
Positive vs negative field direction? ▾
Field lines point away from positive charges, toward negative.
Superposition principle? ▾
Total field from multiple charges = vector sum of individual fields.