D.2. Electric and Magnetic Fields

Formulae and Definitions

Electric Charge (Coulomb)

Conductors

Conductors contain plenty of free electrons which can move when an electric field is present.

Insulators

Insulators contain very few free electrons, thus inhibiting the electric field.

Conservation of Charge

The total charge of an isolated system is conserved, and cannot change.

Coulomb’s Law

Electric Field

Force per unit charge experienced by a small positive test charge q.

The closer the field lines, the stronger the field.

Electric Field Strength (Small Positive Test Charge)

Electric Field Strength (Two Charges)

Electrostatic Charge

In electrostatics, the electric field is zero inside a conductor. This is because electrostatics deals with situations in which the charge doesn’t move. If the electric field existed inside a conductor, it would force charges to move.