Fundamentals of Electric Dipoles and Current

Electric dipole

Two equal and opposite charges separated by a small distance.

Permanent electric dipole

A permanent dipole has a constant separation of charges.

Induced electric dipole

An induced dipole forms temporarily in response to an external electric field.

Good solvent property of water

Because it has a permanent electric dipole that allows it to interact with and dissolve polar substances.

Dipole in a uniform electric field

It experiences no net force but does experience a torque.

Electric current

I = dQ/dt

Conventional current

A flow of positive charges (opposite to electron flow in metals).

Charge movement in a conductor

An electric field.

Drift velocity

The average velocity of charge carriers in a conductor.

Current density (J)

Current per unit area: J = I/A.

Resistivity formula

ρ = E/J.

Resistance formula

R = ρL/A.

Ohm's Law

V = IR.

Ohmic materials

Ohmic materials have constant resistance.

Non-ohmic materials

Non-ohmic materials do not obey Ohm's Law.

Electromotive force (EMF)

Energy per unit charge provided by a source; not an actual force.

Terminal voltage calculation

V_ab = ε - Ir.

Voltmeter connection

In parallel.

Ammeter connection

In series.

Power formulas for a resistor

P = I²R

Short circuit danger

It can cause excessive current

Kirchhoff's Junction Rule

The total current into a junction equals the total current out: ∑I = 0.

Kirchhoff's Loop Rule

The total voltage change around a closed loop is zero: ∑V = 0.

Sign convention for voltages in loops

Positive when moving with potential drop or emf; negative when moving against.