EMC Question of the Week: July 17, 2017

Circuit consisting of four resistors forming a loop

The algebraic sum of all the voltages around any closed path in a circuit equals zero.

  1. true
  2. false

Answer

Electrical engineers will recognize the sentence above as a statement of Kirchhoff's Voltage Law (KVL). Nevertheless, if we are talking about real implementations of circuits, the correct answer is b.) false. KVL is a very useful concept and a cornerstone of circuit theory. Unfortunately, circuit theory doesn't always apply to real implementations of circuits. Circuits (and everything else in the known universe) comply with Maxwell's equations.

Faraday's Law (one of Maxwell's equations) effectively says that the sum of all the voltages around any closed path will equal the time rate of change of the magnetic flux passing through the loop formed by the closed path. At DC this will be zero, but at higher frequencies it may not be zero. This concept is very important to EMC and signal integrity engineers when considering issues related to parasitic inductance or magnetic field coupling. For more information, see Faraday's Law for EMC Engineers. 

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