Electric Charge Signs - Electric Fields, Electrostatics & Capacitors Step by Step

Electric charge has a sign. That sign is part of the physical source and determines the direction rule for electric forces.

electrostatics Positive and negative charge are source signs, not just colors in a diagram.

Example

Electric charge has a sign. That sign is part of the physical source and determines the direction rule for electric forces. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Charge has a sign

Electric charge comes with a sign. A positive charge and a negative charge are different source types, not just different colors in a picture.

q > \text{zero} \quad \text{or} \quad q < \text{zero}

The value includes the unit

The left charge is positive 2 coulombs. The right charge is negative 3 coulombs. The sign belongs to the charge value.

q_{\text{left}} = +2\ \text{C}\qquad q_{\text{right}} = -3\ \text{C}

Signs decide force direction

A charge sign does not say how strong the force is by itself. It sets the direction rule: matching signs push apart, opposite signs pull together.

\text{same signs repel} \qquad \text{opposite signs attract}

The sign rule has only two outcomes

Scan the sign pairs before thinking about size. Matching signs repel; opposite signs attract. The diagram shows one positive and one negative source, while the table lists the rule.

\begin{array}{c|c|c}q_{\text{left}}&q_{\text{right}}&\text{force direction}\\+&+&\text{repel}\\-&-&\text{repel}\\+&-&\text{attract}\end{array}