Physics

• Charge

  A property of matter that causes it to experience an electrical force when it has been placed in an electric field
• Current

  The rate of flow of charge
• Current is measured in amps, charge is measured in coulombs, and time is measured in seconds
• Charge is quantized, meaning it comes in tiny indivisible individual quantities
• Elementary charge

  The smallest unit of charge, approximately 1.6 x 10^-19 coulombs
• Electron charge is -1.6 x 10^-19 coulombs, proton charge is +1.6 x 10^-19 coulombs
• In conductors, the charge carriers are free electrons, in electrolytes the charge carriers are positive and negative ions
• Conventional current is defined as flowing from positive to negative, even though electron flow is from negative to positive
• Kirchhoff's first law

  The sum of the currents entering a junction equals the sum of the currents exiting a junction
• Kirchhoff's first law is a statement of conservation of charge
• Number density

  The amount of charge carriers per unit volume
• Drift velocity

  The average displacement per unit time of charge carriers along a conductor
• Conductors have a high number density of charge carriers, insulators have a low number density, semiconductors have an intermediate number density