Important Formulas and Equations in Electrical Engineering

Ohm's Law:
- V = IR
- I = V/R
- R = V/I

Power:
- P = VI
- P = I^2R
- P = V^2/R

AC Circuits:
- Impedance (Z) = R + jX
- Complex Power (S) = P + jQ
- Power Factor (PF) = P/S
- Apparent Power (|S|) = VI
- Reactive Power (Q) = |S|sin(θ)
- True Power (P) = |S|cos(θ)

Transformers:
- Turns Ratio (N1/N2) = V1/V2 = I2/I1
- Voltage Ratio (V1/V2) = N1/N2
- Current Ratio (I2/I1) = N1/N2

Three-Phase Systems:
- Line Voltage (VL) = √3 × Phase Voltage (VP)
- Line Current (IL) = Phase Current (IP)
- Power (P) = √3 × VLine × ILine × Power Factor (PF)

Inductors and Capacitors:
- Inductive Reactance (XL) = 2πfL
- Capacitive Reactance (XC) = 1/(2πfC)
- Impedance of an Inductor (XL) = j2πfL
- Impedance of a Capacitor (XC) = -j/(2πfC)

Network Theorems:
- Kirchhoff's Voltage Law (KVL): The sum of the voltages around a closed loop in a circuit is zero.
- Kirchhoff's Current Law (KCL): The sum of the currents entering a node in a circuit is equal to the sum of the currents leaving the node.
- Thevenin's Theorem: Any linear bilateral network containing several voltage and/or current sources can be replaced by an equivalent circuit consisting of a single voltage source (Thevenin voltage) in series with an impedance (Thevenin impedance).
- Norton's Theorem: Any linear bilateral network containing several voltage and/or current sources can be replaced by an equivalent circuit consisting of a single current source (Norton current) in parallel with an impedance (Norton impedance).

Other Important Equations:
- Coulomb's Law: F = k(q1q2)/r^2
- Gauss's Law: ∮E.dA = q/ε₀
- Faraday's Law: ∮E.dl = -dφB/dt
- Ampere's Law: ∮B.dl = μ₀I + μ₀ε₀(dφE/dt)

These are some of the important formulas and equations that are commonly used in electrical engineering. Understanding and memorizing these equations will help in solving problems and analyzing electrical circuits.