What are electric field lines and what do they represent?

Electric field lines are imaginary curves that show the direction a positive test charge would move if placed in the field. They originate from positive charges and terminate on negative charges. The density of field lines indicates the field strength — closer lines mean a stronger field. Field lines never cross because the electric field has a unique direction at every point in space.

What is an equipotential surface and why is it perpendicular to field lines?

An equipotential surface is a set of points where the electric potential has the same value. No work is done when moving a charge along an equipotential surface because there is no potential difference. Equipotential surfaces are always perpendicular to electric field lines because the electric field points in the direction of the steepest decrease in potential, which is always normal to surfaces of constant potential.

How does the superposition principle apply to electric fields?

The superposition principle states that the total electric field at any point is the vector sum of the individual electric fields produced by each charge. This means you calculate E = kq/r² for each charge separately (with direction), then add all the vectors tip-to-tail. This principle works because Maxwell's equations are linear, so solutions can be added together.

Electric Field Simulator

Place positive and negative charges to visualize electric field lines, equipotential surfaces, and the superposition of fields in real time.

Charges

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Field Lines Equipotential Field Vectors Test Charge

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Properties

Number of Charges	—
Net Charge	—
Field Magnitude	—
Field Direction	—
Potential	—

The Physics Behind It

Coulomb's Law & Electric Field

Coulomb's Law: F = k q₁ q₂ / r²
Electric field of a point charge: E = k q / r²
Coulomb constant: k = 8.99 × 10⁹ N·m²/C²
Direction: field points away from positive charges and toward negative charges
Field lines never cross — the field has a unique direction at every point

Superposition & Potential

Superposition principle: E⃗ₙₓₙ = Σ E⃗ᵢ — fields from multiple charges add as vectors
Electric potential: V = k q / r (scalar, not a vector)
Equipotential lines are perpendicular to field lines at every point
No work is done moving a charge along an equipotential surface
A dipole (equal and opposite charges) produces the classic two-lobed field pattern

Electric Field Simulator

Charges

Properties

The Physics Behind It

Coulomb's Law & Electric Field

Superposition & Potential

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