Applied Electromagnetics Using QuickField and MATLAB

Chapter 13 - Electrical Circuits: Electrical Current and Ohm's Law

In This Chapter

  • Electrical Current and Ohm’s Law
  • Kirchhoff ’s Laws
  • Resistances in Parallel and Series
  • Capacitances in Parallel and Series
  • Impedances in AC Circuits
  • Transient Currents in Electrical Circuits
  • Electrical Circuit Modeling in QuickField
  • Filter Applications
  • Electrical Circuit Models of Biological Systems
  • Chua’s Chaotic Circuit

Electrical current I is defined as the total charge that flows through a conductor per unit time or

The SI unit of current is the Ampere (A) defined as a Coulomb (C) per second. Benjamin Franklin first adopted the convention that current flows in the direction of positive charge. The motion of negative charge to the left is equivalent to a positive current flow to the right. The charge carriers in a circuit are usually negatively charged electrons, hence the direction of current is taken as opposite to the direction of electron flow. Current flows in proportion to the potential drop V across a conductor and in inverse proportion to the materials resistance R according to Ohm's law

Electrical resistance results from the scattering of electrons by the crystal lattice, phonons, and impurities in a conductor. The unit of resistance is the Ohm (Ω) defined as a volt per Ampere. Experimentally Ohm found that resistance is proportional to the length L and inversely proportional to the cross-sectional area S of a conductor

The resistivity ρ is a material property that is geometry independent with S.I. units of Ω • m. Most metals are good conductors of electricity. Resistivity decreases with lower temperature and becomes identically zero below a transition temperature Tcin superconductors. In poorly conducting nonmetals, or insulators, electrons are strongly bound to positive nuclear charges and are not free to move.

 

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