Charge
Capacitor

Coulomb's law, force of attraction/repulsion
F = kQ₁Q₂/r²
   Q₁ and Q₂ are the charges in coulombs
   F is force in newtons
   r is separation in meters
   k = 8.99e9 Nm²/C²
   k = 1/(4πε₀)
    where ε₀ = 8.8542e-12 F/m = permittivity of
    space (F/m)

in presence of dielectric, that is modified to
F = Q₁Q₂/(4πε₀εᵣr²)
or F = kQ₁Q₂/(εᵣr²)
   εᵣ is dielectric constant (vacuum = 1)

Potential energy between two charges, in Joules
U = kQ₁Q₂/r
   Q₁ and Q₂ are the charges in coulombs
   r is separation in meters
   k = 8.99e9 Nm²/C²
between three charges it is
U = (kQ₁Q₂/r₁₂) + (kQ₂Q₃/r₂₃) + (kQ₁Q₃/r₁₃)
    (assume – for unlike charges)

Charge moving in an electric field
E = QV
1 coulomb moving thru a 1 volt change = 1 J

Electric field
The strength or magnitude of the field at a given point
is defined as the force that would be exerted on a
positive test charge of 1 coulomb placed at that point;
the direction of the field is given by the direction of
that force.
   E = F/Q = kQ/r²
   Q = F/E   F = QE
in Newtons/coulomb OR volts/meter
   k = 1/4πε₀ = 8.99e9 Nm²/C²
1 C = 6.242e18 electrons
1 electron charge = 1.602e-19 C

Potential from a charge is
V = kQ/r in volts
   k = 1/4πε₀ = 8.99e9 Nm²/C²
   r is separation in meters
   q is charge in coulombs

Energy in a particle
E = hf, where h = Plank's constant 6.626e-34 Js
E = hc/λ
  E is the energy of the particle in Joules
  f is frequency, λ is wavelength in meters


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