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
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