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.

∑I_Entering = ∑I_Leaving

∑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

• You may find more about KVL & KCL Here.

Coulomb’s Law

Coulomb’s laws of electrostatics provides the force of attraction or repulsion between two charges or charged bodies.

or

• F = force of repulsion or attraction between charges
• ε₀ = permittivity in space
• ε_r = relative permittivity of material
• q₁, q₂ = 1^st & 2^nd amount of charge respectively in coulombs
• r = Distance between the charges in meters
• k = constant

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