Electrostatics

We start with a few concepts about electric charge and how they behave when they are at rest. Later we will study their movement in electric currents.

Charge

• Charge is the net sum of electrons and protons
• If there are more electrons than protons, an item has a negative charge
• Charge is measured in coulombs
• A coulomb is approximately 6.2 \cdot 10^{18} electrons of charge.
• We also measure charge in ampere-hours when we are talking about batteries.
• Charge is conserved

Electrons

• Charge movement is the movement of the electrons
• The protons stay fixed in the nucleus

Force between Charges

• Coulombs law quantifies the force between two charges
• It requires energy to move an object against a force
• This so, moving a charge requires energy that is stored as potential energy
• This energy is related to voltage

Voltage

• When charge moves to a higher or lower voltage it gains or loses energy.
• Voltage is the joules per coulomb of energy gained or lost
• Height is a good mental model
• One coulomb of charge raised to a potential of one volt gains one Joule of energy