Current and Charge

• Electric current is the rate of flow of charge, measured in Amps (A)
• Equation for current (with time):

  $current =$$charge/time$
• 1A is the same as one coulomb of charge passing a given point per second (1Cs^-1)
• A coulomb is the electric charge flowing past a point in one second when there is an electric current of one amp.
• Possible charge carriers:

  • Electrons - in metals
  • Ions - in electrolytes
• Conventional current is the flow of charge carriers from the positive terminal to the negative.
• Kirchoff's first law states that the sum of the current going into a junction is equal to the sum of the current leaving the junction
• Mean drift velocity is the average velocity of the charge carriers.

  
  

  Equation is:

  
  

  I = nAve
• A charge carrier is any particle with carries electric charge
• elementary charge is 1.60x10^-19
• Charge carriers in liquids tend to be ions
• Charge carriers in metals are electrons
• A larger current may be due to a greater number of electrons moving past a given point each second

  The same number of electrons moving faster through metal
• Flow of electrons in a circuit is from the negative terminal to the positive
• Ammeters are used to measure the electric current any part of the circuit, placed in series
• An ideal ammeter will have the lowest possible resistance to reduce the effect they have on the current.
• Conservation of charge, electric charge can not be created or destroyed
• Number density is the number of free electrons per cubic meter of material
• Semiconductors have a much lower number density than metals, so in order to maintain the same current, the electrons in semiconductors need to move faster.