Voltage is the difference in charge between two points. It is measured in volts, and represented in equations and schematics by the letter V.

Current is the rate at which charge is flowing. Current is measured in Amperes (usually just referred to as “Amps”). Amps are represented in equations by the letter I.

Resistance is a material’s tendency to resist the flow of charge (current). Unit of resistance is “1 Ohm”, defined as the resistance between two points in a conductor where the application of 1 volt will push 1 ampere, or 6.241×10^18 electrons. This value is usually represented in schematics with the greek letter Ω, which is called omega, and pronounced “ohm”.

Ohm’s Law

Combining the elements of voltage, current, and resistance, Ohm developed the formula:

V = I * R


  • V = Voltage in volts
  • I = Current in amps
  • R = Resistance in ohms

Kirchhoff’s First Law

Summation of all Current in any point of circuit equals to 0.

Kirchhoff’s Second Law

Summation of all Voltage in any Loop always equals to 0.

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