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Field of a point charge
Beginner
Field decreases as inverse square.
E = kq/r²E = kq/r², directed away from a positive charge and toward a negative one. It follows an inverse-square law.
1 nC at 1 m: 9 N/C.
Superpose vectorially for multiple charges.
In more detail
The field of a point charge is E = kq/r², pointing away from a positive charge and towards a negative charge. It falls with the inverse square of distance.
Real-world uses
- Estimating fields around charged particles in detectors.
- Modelling ions in electrolytes.
- Engineers estimate the field near a charged sphere, such as a lightning conductor, to judge where sparks will form.
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Frequently asked questions
Is the field zero at the charge?
The field is undefined at the point charge itself, though it grows without bound as r approaches zero.
Does the direction depend on the sign?
Yes, it points outward for positive and inward for negative charges.
Why does the field fall off so quickly?
It follows the inverse square law, so doubling the distance cuts the field to a quarter.
Related topics in Electrostatics
Coulomb constant · Superposition of forces · Electric field · Electric field lines · Electric dipole · Field of a dipole