Field Vector Direction - Electric Fields, Electrostatics & Capacitors Step by Step

A field vector is a local direction claim. Positive sources point away; negative sources point toward.

electrostatics The source sign sets the field direction before any test charge size is chosen.

Example

A field vector is a local direction claim. Positive sources point away; negative sources point toward. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Field points away from positive charge

Use a positive 1 coulomb test charge. Near a positive source, the field arrow points away from the source.

+\text{ source} \Rightarrow E \text{ points away}

Field points toward negative charge

Use the same positive test charge near a negative source. The field arrow points toward the negative source.

-\text{ source} \Rightarrow E \text{ points toward}

Direction changes even when size matches

Both examples use a field size of 4 newtons per coulomb. The size matches, but the source sign changes the direction.

E = 4\ \text{N/C}\qquad \text{source sign sets direction}

Sign changes direction, not the local unit

Both rows still measure field in newtons per coulomb. The source sign chooses whether the arrow points away from the source or toward it.

\begin{array}{c|c|c}\text{source sign}&\text{field direction}&\text{positive test force}\\+&\text{away}&\text{with field}\\-&\text{toward}&\text{with field}\end{array}