PhysicsElectric FieldsA-Level
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Electric Field Strength (Point charge) Calculator

Force per unit charge in a radial electric field.

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Electric Field Strength

Formula first

Overview

This equation calculates the magnitude of the electric field intensity generated by a stationary point charge at a specific distance in a vacuum. It describes a fundamental inverse-square relationship where the strength of the field diminishes rapidly as one moves away from the source charge.

Symbols

Variables

E = Electric Field Strength, Q = Point Charge, \varepsilon_0 = Permittivity of Free Space, r = Distance

Electric Field Strength
Point Charge
Permittivity of Free Space
Distance

Apply it well

When To Use

When to use: Use this formula when analyzing the electrostatic force per unit charge exerted by an isolated point charge or a spherically symmetric charge distribution. It is intended for use in vacuum or air, assuming the charge is stationary and localized at a single point in space.

Why it matters: Understanding point charge fields allows scientists to model the behavior of subatomic particles, design laboratory equipment like mass spectrometers, and calculate the forces involved in chemical bonding. It serves as the foundation for the principle of superposition, which is used to solve for complex electric fields in engineering.

Avoid these traps

Common Mistakes

  • Using distance completely instead of squared distance.

One free problem

Practice Problem

Calculate the electric field strength E at a point 2.0 meters away from a point charge Q of 5.0 × 10⁻⁶ C in a vacuum.

Point Charge0.000005 C
Distance2 m
Permittivity of Free Space8.854e-12 F/m

Solve for:

Hint: Square the distance in the denominator and use the value of pi as 3.14159.

The full worked solution stays in the interactive walkthrough.

References

Sources

  1. Fundamentals of Physics by Halliday, Resnick, and Walker
  2. Introduction to Electrodynamics by David J. Griffiths
  3. Wikipedia: Electric field
  4. NIST CODATA 2018 (for ε0 value)
  5. Halliday, Resnick, Walker, Fundamentals of Physics, 11th Edition
  6. Griffiths, Introduction to Electrodynamics, 4th Edition
  7. Halliday, Resnick, Walker, Fundamentals of Physics, 11th ed., John Wiley & Sons, 2018.
  8. Griffiths, David J., Introduction to Electrodynamics, 4th ed., Pearson, 2013.