Electromagnetism
Essential formulas and concepts in electromagnetism
Coulomb’s Law
Variables:
Description/Usage:
Gives the electrostatic force between two charges. The force is attractive if charges are opposite, repulsive if like-signed. It is an inverse-square law similar in form to gravity.
Electric Field of Point Charge
Variables:
- \(q = source charge, r = distance from the charge, E = electric field magnitude at that distance (radially outward for q>0, inward for q<0).\)
Description/Usage:
The electric field is force per unit charge. For a point charge, it diminishes with distance squared.
Electric Potential (Point Charge)
Variables:
- \(q = point charge, r = distance from the charge, V = electric potential (voltage) at that point relative to infinity.\)
Description/Usage:
The electric potential is the potential energy per unit charge. For a point charge, it falls off as \(1/r\). Differences in \(V\) between two points give the work per charge to move between those points.
Capacitance (Parallel Plate)
Variables:
Description/Usage:
Capacitance is the ability to store charge per unit voltage (\(C=Q/V\)). For parallel plates, larger area or smaller gap yields bigger \(C\). This formula is a basic design equation for capacitors.
Ohm’s Law
Variables:
- \(V = voltage (potential difference across a resistor or circuit element), I = current through it, R = resistance.\)
Description/Usage:
Electrical Power
Variables:
- \(P = power (rate of electrical energy consumption or production), V = voltage across a component, I = current through it, R = resistance (if using that form).\)
Description/Usage:
Different forms of the power formula useful depending on known quantities. For instance, a 60 W light bulb on household 120 V draws \(I = P/V = 0.5\) A. The formulas also explain joule heating: \(I^2R\) is heat dissipated in a resistor.