Electric Field Calculator

What Is Electric Field?

The electric field $\mathbf{E}$ at a point describes the force per unit charge that a positive test charge would experience. For a point charge $q$ at distance $r$, the magnitude is:

$$\mathbf{E} = k\frac{q}{r^2}$$

where $k \approx 8.99 \times 10^9\ \mathrm{N \cdot m^2/C^2}$ is Coulomb's constant. In a dielectric medium with relative permittivity $\varepsilon_r$, the effective constant becomes $k_{\mathrm{eff}} = k / \varepsilon_r$.

Vector Superposition

When multiple point charges are present, the net field is the vector sum of individual contributions. Each charge $q_i$ at position $(x_i, y_i)$ contributes:

$$E_x = \sum_i k_{\mathrm{eff}} \frac{q_i (x - x_i)}{r_i^3}, \quad E_y = \sum_i k_{\mathrm{eff}} \frac{q_i (y - y_i)}{r_i^3}$$

Electric potential $V$ at a point is the scalar sum $V = \sum_i k_{\mathrm{eff}} q_i / r_i$.

Frequently Asked Questions

Are V/m and N/C the same unit for electric field?

Yes. One volt per meter equals one newton per coulomb. Both measure electric field strength.

How does dielectric material affect the field?

A medium with higher relative permittivity $\varepsilon_r$ reduces the field strength by a factor of $\varepsilon_r$ because the material partially screens the source charge.

Can I solve for charge or distance instead of E?

Yes. In single-charge mode, select whether to solve for electric field, source charge, or distance. The tool rearranges $E = kq/r^2$ automatically.

What happens at the exact location of a charge?

The field of a point charge is undefined at $r = 0$. Place the test point away from source charge positions in multi-charge mode.

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What Is Electric Field?

Vector Superposition

Frequently Asked Questions

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