4.1 Charge and Current

• What is Charge(Q)

  A quantity that objects possess that can be positive or negative.
• What is a Coulomb(C)

  The unit of charge where one Coulomb is the charge carried by 1 amp in 1 second.
• What is the Elementary Charge(e)

  The smallest amount of charge an object can possess. e = 1.6x10^-19
• The charge on an electron

  -e
• The charge on a proton

  +e
• What is meant by Quantisation of Charge


  The charge on any object can only be an integer multiple of e
• What is current(I)

  The rate of flow of electrical charge.
• What is an amp(A)

  The unit of current where one amp carries 1 coulomb past a point every second.
• What is meant by a charge carrier

  A charge partical that carries
• What is mean drift velocity

  The average displacement travelled by free charge carriers along the wire per second.
• $I =$$nAve$

  • I = Current
  • n = Number density of free charge carriers
  • A = Cross sectional area
  • v = Mean drift velocity
  • e = Charge of one charge carrier
• What is number density

  The number of free charge carriers per unit volume.
• What is the unit of number density

  m^-3
• The larger the value for n for a material the better electrical conductor that material is
• Number density of conductors

  n = 10^28 - 10^30
• Number density of semi-conductors

  n = 10^10 - 10^20
• Number density of Insulators

  n is close to 0
• What is the equation that relates Current, Time and Charge

  $I =$$ΔQ/Δ t$
• What is conventional current

  The direction of flow of positive charge.
• How does conventional current differ from charge carrier flow

  If the charge carriers have negative charge then the charge carrier flow has the opposite direction of conventional current.
• Kirchoff's First Law

  The sum of currents into a junction = the sum of currents out of a junction.
• Kirchoff's first law is an example of the law of conservation of charge.