Charge & current

• Current --> the rate of transfer of charge
• Kirchoff's 1st law --> At a junction in an electrical circuit, the sum of currents flowing into the junction is equal to the sum of the currents flowing out the junction
• I1 + I2 = I3 + I4 + I5
• Drift velocity --> The average displacement per unit time of charge carriers along the conductor
• Current = number of charge carriers x cross sectional area x drift velocity x electron charge

  I= nAve

  I in amps

  n in m^-3

  A in m^2

  v in ms^-1

  e in C
• Conductors --> high value of n (number density)
• Semiconductors --> intermediate value of n
• Insulators --> low value of n
• Kirchoff's 1st law is a statement of conservation of charge
• Number density --> the amount of charge carriers per unit volume
• Number density (m^-3) = number of charge carriers/ volume (m^3)