 # Formula & Equations for Ohm’s, Kirchhoff’s & Coulomb’s Laws

## Ohm’s Law, Kirchhoff’s Laws (KVL & KCL ) & Coulombs Laws Formulas & Equations ### Ohm’s Law Formulas

Ohm’s law shows the relationship between current “I” & the voltage “V” where the resistance “R” is a constant in an electrical circuit.

Ohm’s Law in DC Circuits

• I = V/R            For current calculation
• V = IR             For voltage calculation
• R = V/I            For resistance calculation

Ohm’s Law in AC Circuits

• I = V/Z             For current calculation
• V = IZ              For voltage calculation
• Z = V/I             For impedance calculation

Where

• I = Current in Amperes (A)
• V = Voltage in Volts (V)
• R = Resistance in Ohms (Ω)
• Z = Impedance in Ohms (Ω)

### Kirchhoff’s Current Law – KCL

Summation of all currents entering a node or junction is 0. Or the sum of entering and leaving currents  at a point is zero. In other words, the current entering at a point is equal to the current leaving that point. ∑IEntering = ∑ILeaving

∑I = 0

• Current entering the node is denoted with positive sign (+).
• Current leaving the node is written with a negative sign (-).

### Kirchhoff’s Voltage Law – KVL

Summation of all potential differences in a circuit loop is 0. The product of I “Current” and R “Resistance” in a closed path (also known as mesh) located in a network is equal to the applied EMF. IR = ∑E

### Coulomb’s Law

Coulomb’s laws of electrostatics provides the force of attraction or repulsion between two charges or charged bodies. • F = force of repulsion or attraction between charges
• ε0 = permittivity in space
• εr = relative permittivity of material
• q1, q2 = 1st & 2nd amount of charge respectively in coulombs
• r = Distance between the charges in meters
• k = constant

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