Physics 2

• current


  any motion of charge from one region to another
• current


  amount of charge flowing through a specified area, per unit time
• direct current


  the direction of the current does not change with time
• alternating current


  the current oscillates back and forth
• current density


  current per unit cross-sectional area
• a charged particle inside the conducting material is subjected to a steady force
• if the charged particle is moving in vacuum, the steady force would cause a steady acceleration in the direction of the force
• a charged particle moving in a conducting material undergoes frequent collisions with the ions of the material, in each collision the particle's direction undergoes random change
• drift velocity


  a very slow net motion of the moving charged particle in the direction of the electric force
• resistivity


  the ratio of the magnitude of the electric field and current density
• good conductors have small resistivity, good insulators have large resistivity
• the potential difference of a material is proportional to the current in the sample [according to ohm's law]
• resistor


  a circuit device made to have a specific value of resistance between its ends
• for a conductor to have a steady current, it must be part of a path that forms a closed loop or complete circuit
• complete circuit


  has continuous current-carrying path
• a complete circuit carrying a steady current must contain a source of electromotive force
• electromotive force


  the influence that makes current flow from lower to higher potential
• emf source


  a circuit device that provides emf
• every real source of emf has some internal resistance, so its potential difference depends on the current
• non-ideal source


  the potential difference across a real source in a circuit is not equal to the emf
• $V(ab)=$$ɛ - Ir$


  v(ab) = voltage

  ɛ = emf

  I = current

  r = resistance
• the current in a simple loop is the same at every point
• the current depends on both the internal resistance r and the resistance of the external circuit
• in a short circuit, the external-circuit resistance is zero, because terminals of the battery are connected directly to each other.
• a current puts energy into a circuit if the current direction is from a lower to higher potential in the device
• a current takes energy from a circuit if the current direction is from a higher to lower potential in the device
• a resistor always takes electrical energy out of a circuit
• as charge passes through the circuit element, the electric field does work on the charge
• resistors in series


  the current is the same for all resistors
• resistors in parallel


  the current is different for each resistor
• resistors in parallel


  the potential difference between the terminals of each resistor must be the same and equal to Vab
• kirchhoff's junction rule

  based on conservation of charge
• kirchhoff's junction rule


  as much current flows into a junction as it flows out of it
• kirchhoff's junction rule


  the algebraic sum of all the currents in a junction is zero
• kirchhoff's loop rule


  the algebraic sum of potential differences in a loop is zero
• ammeter


  a current-measuring instrument
• voltmeter


  used to measure potential difference or voltage
• ohmmeter


  instrument that measures resistance
• multimeter


  an instrument that can measure voltage, current, or resistance over a wide range
• rc circuit 


  a circuit that has a resistor and capacitor in series