CHAP 5: DIRECT-CURRENT CIRCUITS

• refers to the unidirectional propagation of electric charge. The flow of electric charge does not change direction. Direct current is produced by batteries, fuel cells, rectifiers, and generators with commutators.


  Direct current
• If the resistors are in series, the current 𝐼 must be the same in all of them
• The equivalent resistance of any number of resistors in series equals the sum of their individual resistances.
• If the resistors are in parallel, the potential difference between the terminals of each resistor must be the same.
• For any number of resistors in parallel, the reciprocal of the equivalent resistance equals the sum of the reciprocals of their individual resistances.
• To compute the currents in these networks, we’ll use the techniques developed by the German physicist Gustav Robert Kirchhoff (1824–1887).
• Kirchhoff’s junction rule: The algebraic sum of the currents into any junction is zero.
• a point where three or more conductors meet.


  Junction
• Kirchhoff’s loop rule: The algebraic sum of the potential differences in any loop, including those associated with emfs and those of resistive elements, must equal zero.
• any closed conducting path.


  Loop
• Sign Conventions for the Loop Rule:

  (a) Sign of convention for emfs

  (b) Sign of conventions for resistors