SUMMARY

• The atom is the smallest part of a matter.
  
  
• The International System of Units has seven base units, several derived units with special names, and many derived units with compound names.
  
  
• Basic parts of an atom are the proton, electron, and neutron.
  
  
• The presence of charge implies that there is an electric force field.
  
  
• The system of units most commonly used in electrical engineering is the SI.
  
  
• The work required moving a unit charge in electric field is a measure of potential difference or voltage difference. Potential difference is measured in units of volts.
  
  
• To define a current, both a value and a direction must be available.
  
  
• To define a voltage across an element, it is necessary to label the terminals with “+” and “-“ signs as well as to provide a value.
  
  
• Any element is said to supply positive power if the positive current flows out of the positive voltage terminal. Any element absorbs positive power if positive current flows into the positive voltage terminal.
  
  
• Wires are typically assumed to have zero resistance in circuit analysis.
  
  
• A ground is a conductor that may be used as a reference conductor. A reference conductor may or may not be connected to Earth.
  
  
• A branch is a single two-terminal element in an electric circuit. A node in an electrical circuit is a point at which two or more circuit elements are joined together. A loop is a closed path in a circuit. The number of branches b, the number of nodes n, and the number of independent loops l in a network are related by the following equation:

• Some circuits may be solved by combining resistances in series and/or parallel. A last simple circuit is obtained and Ohm’s law may be applied to find voltage and current in the simplified circuit. The results are transferred back through the chain of equivalent circuits. The current and voltages of interest in the original circuit can be found.
  
  
• Capacitors store electric field energy. The use of dielectrics between the plates of the capacitor increases the charge that can be stored. When electric displacement density D is changing in a capacitor it is analogous to current flow. This current is called a displacement current.
  
  
• Inductors are devices that are designed to store magnetic field energy.
  
  
• A steady flow of charge is a current measured in amperes. The relationship between resistance, voltage, and current is Ohm’s law.