• Charge is measured in?coulombs?(C). One coulomb is defined as:

The charge carried by an electric current of one ampere in one second

• Charge is a?scalar?quantity
  • Electrons?have a?negative charge
  • Protons?have a?positive charge
• Like charges?repel?each other and?attract?opposite ones
• In?neutral?(i.e.?uncharged) atoms and objects the number of electrons and the number of protons are equal
• The?movement of electrons?determines the charge of an atom or object
• In?charged?atoms or objects there is a net amount of either positive or negative charge
  • An object that?gains electrons?has an overall negative charge
  • An object that?loses electrons?has an overall positive charge

• In?conductors, some electrons are free to move between atoms

Delocalised electrons in the outer shell of the atoms in a conductor can move between atoms. When a neutral atom loses electrons it becomes a positive ion

• The?electric current?through a conductive material is defined as follows:

The rate of flow of electric charge past a cross-section of material

• Current is measured in?amperes?(A)
  • The ampere is a?fundamental unit?of the?SI?system

• Current is calculated as follows:

• Where:
  • I?= current in amperes (A)
  • Δq?= net charge flowing past a cross-section of material in coulombs (C)
  • Δt?= time interval in seconds (s)
• The conventional?direction?of current is?from positive to negative
  • Electrons flow opposite to the conventional direction of current

By definition, conventional current always goes from positive to negative (even through electrons go the other way)

Step 1: Write down the known quantities

• • Δq?= 20 μC = 20 × 10^–6?C
  • Δt?= 60 ms = 60?× 10^–3?s

Note the conversions:

• • The amount of charge must be converted from micro coulombs (μC) into coulombs (C)
  • The time must be converted from milliseconds (ms) into seconds (s)

Step 2: Write down the equation for the electric current?I

Step 3: Substitute the numbers into the equation

I?= 3.3 × 10^–4?A