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
for a constant electric field
Ed = Fd/q = W/q = ΔV
E is electric field
d is distance moved
F is force
q is charge
W is work done
V is voltage
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 is
The work per unit of charge required to move a charge from a
reference point to a specified point, measured in joules per coulomb
or volts. reference point is usually infinity. The electric potential
for a system of point charges is equal to the sum of the point
charges' individual potentials.
The 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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