In this section we learn how electric fields tell us where a positive charge will feel a push or pull. The key idea is that the electric field at any point points in the direction a positive test charge would be pushed.
Think of an electric field like a wind that pushes a tiny kite (the positive charge). If you place a kite in a wind, it will move in the direction the wind blows. The same happens to a positive charge in an electric field.
The direction of the electric field at a point is defined as the direction of the force that would act on a small positive test charge placed at that point.
Mathematically, if the force on a test charge \$q0\$ is \$\mathbf{F} = q0 \mathbf{E}\$, then the field vector \$\mathbf{E}\$ points in the same direction as \$\mathbf{F}\$ when \$q_0>0\$.
Imagine two charges: \$+Q\$ at the left and \$-Q\$ at the right. Where does the electric field point at the midpoint?
| Position | Field Direction | Reason |
|---|---|---|
| Midpoint between +Q and -Q | Rightwards (towards \$-Q\$) | Field from \$+Q\$ points right, from \$-Q\$ points left; they cancel, leaving the rightward component from \$+Q\$ dominant. |
Remember: The electric field tells you the “push” direction for a positive charge. If you flip the charge to negative, the force reverses, but the field itself stays the same.