a branch of physics that studies electric charges at rest.
Coulomb's Law Formula
F — force of interaction between point charges; q₁ and q₂ — magnitudes of charges, r — distance between them; k — proportionality constant: 9·10⁹ N·m²/C². The force decreases inversely proportional to the square of the distance.
Formula for electric field strength
E — electric field strength created by charge q at distance r. Shows the force the field exerts on a unit positive charge. Vector E points away from a positive charge, towards a negative one — by definition of the field.
Formula for the work of the electric field
A — work done to move charge q in a uniform field E over distance d. If movement is along the field — work is positive, against the field — negative. Related to the change in potential energy.
Formula for the potential energy of interaction of two charges
Energy of interaction between two charges at distance r. As distance tends to infinity, energy tends to zero. Sign depends on the signs of charges: attraction or repulsion.
Formula for electric potential
Potential — energy per unit positive charge. k·q/r — formula for a point charge, E·d — for a uniform field. Relative quantity: defined relative to a chosen point.
Formula for electric field work through potential difference
Movement of charge q between points with potentials φ₁ and φ₂. Work is positive if movement is towards lower potential. Negative — if against the electric field.
Formula for potential energy of charge in an electric field
Energy W = ½·q·φ — this is the energy stored in the electric field created by charge q at potential φ. It does not refer to the potential energy of the charge itself. The factor ½ arises due to the gradual accumulation of charge: as charging proceeds, the potential increases from 0 to φ. The formula describes the work required to fully charge a conductor or capacitor.
Formula for capacitor charge
q — charge on the plates; C — capacitance of the capacitor; U — voltage between the plates. The greater the voltage and capacitance — the greater the stored charge.
Formula for the capacitance of a parallel-plate capacitor
C — capacitance; ε — relative permittivity; ε₀ — electric constant; S — plate area; d — distance between them. The formula shows the dependence of capacitance on geometry and material.
Formulas for the energy of a charged capacitor
W — energy stored in the capacitor's electric field. Formula variants depend on known quantities: capacitance, charge, voltage. Energy is distributed in the volume between the plates.