⚡️ An electric field is a region of space where an electric charge experiences a force. Think of it as an invisible wind that pushes on a tiny ball. If you place a small charged particle in this region, the particle feels a pull or push depending on its charge.
The field is described by the vector quantity \$E\$ (electric field strength). The force on a charge \$q\$ is given by the simple relation:
\$F = qE\$
Key point: If \$q>0\$, the force points in the same direction as the field; if \$q<0\$, it points opposite.
For a single point charge \$Q\$, the electric field at a distance \$r\$ is:
\$E = \frac{1}{4\pi\epsilon_0}\frac{Q}{r^2}\$
Example: Let \$Q = +2\,\mu\text{C}\$ and \$r = 0.1\,\text{m}\$. Using \$\frac{1}{4\pi\epsilon_0} \approx 9.0\times10^9\,\text{N·m}^2/\text{C}^2\$,
The field points radially outward from a positive charge and inward toward a negative charge.
• Always remember that the electric field is defined as the force per unit charge: \$E = \frac{F}{q}\$.
• Check units: the field is measured in newtons per coulomb (N/C).
• When given a force and a charge, you can find the field directly: \$E = F/q\$.
• For point charges, use the inverse square law formula above.
• Pay attention to the sign of the charge – it determines the direction of the field relative to the charge.
1️⃣ If a charge of \$-3\,\text{C}\$ is placed in a field of \$5\,\text{N/C}\$, what is the magnitude and direction of the force?
2️⃣ A point charge of \$+4\,\text{nC}\$ is 0.2 m from a test charge. What is the electric field at that point?
Use the formulas above to solve.