Table of Contents

Electricity

Circuits

Power = watts, current (I) = amps, volts (E or V), resistance (R) = ohms

Resistors in series add together

Resistors in parallel: 1/Rt = 1/R₁ + 1/R₂ + …

current in parallel: if have V, compute R for each path. For two paths, R₁ & R₂: I on R₁ = R₁/(R₁+R₂)

Voltage divider: Vout = R₂/(R₁+R₂) * Vtotal, where R₂ is resistor between Vout and ground

Joules = watts * seconds

Capacitance

Q = CV , Q = charge (coulombs, always a positive value), C = capacitance (farads), V = voltage

Parallel plate capacitor

C = epsilon (A/d), A = area, d = distance between plates
epsilon = permittivity of the dielectric
dielectric constant (over free space) = 8.84 * 10⁻¹² Farads/meter

Electric field E = V/d (volts/meter)

E = sigma/epsilon,  sigma = charge density
sigma = Q/A

Coulomb's law: Find force between two charged objects

F = k * q₁ * q₂ / r²
  k = 9 * 10⁹ N m²/C²
  r = distance in meters
  C = coulombs
  C = Q/V = Q/Ed = A*epsilon/d

Point Charges

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