Chapter 3 | Electricity and Magnetism 2

Distribution, Law of Concentration, Movement of Charges

What are the 3 laws of Electrostatics

Distribution

Charges spread uniformly on a conductor’s surface.

Law of Concentration

Electric charge is greatest at areas with sharp curvature.

Movement of Charges

Only electrons move in solid conductors; protons remain bound in the nucleus.

Solid Conductors, Nucleus

Electrons only move in ; Protons remain bound in the

Electrostatic Force

Attraction between unlike charges or repulsion between like charges; directly proportional to charge magnitude and inversely proportional to the square of the distance.

Electrodynamics

Study of electric charges in motion.

Electrical Engineer

Works with electric current.

Physicist

Studies electron flow.

Electric Current

Movement of electrons along a wire.

Direct Current (DC)

Electrons flow in one direction;

Straight line

Wave form of a direct current

Alternating Current (AC)

Electrons alternate directions; sinusoidal waveform.

Sinusoidal

Wave form of an alternating current

Conductor

Material where electrons flow easily.

Variable resistance; obeys Ohm’s law; needs voltage

Conductor Characteristics

Copper, aluminum, water

Conductor Examples

Insulator

Material that does not allow electron flow.

No electron flow; extremely high resistance; needed for high voltage

Insulator Characteristics

Glass, rubber, clay

Insulator Examples

Semiconductor

Behaves as both conductor and insulator under certain conditions.

Can be conductive or resistive; basis of computers

Semiconductor Characteristics

Silicon, germanium

Semiconductor Examples

Superconductor

Material that conducts with zero resistance.

No resistance, no required potential, must be very cold

Superconductor Characteristics

Niobium, titanium

Superconductor Examples

William Shockley (1946)

Demonstrated semiconduction.

Superconductivity (1911)

Zero resistance below a critical temperature.

Magnetism

Fundamental property of matter; has no smallest unit.

Magnetite (Fe₃O₄)

Naturally magnetic mineral; source of lodestone.

Lodestone

Naturally occurring magnetite that acts as a magnet.

Charged Particle Principle

Any charged particle in motion creates a magnetic field.

Electron Spin

Electron behavior as if rotating; paired spins cancel; unpaired spins create magnetism.

Magnetic Moment

Strength/direction of a magnetic field from a spinning charged particle; basis of MRI.

Magnet

Material producing a magnetic field; always has north & south poles (dipolar).

Magnetic Dipole

Tiny magnet from electron orbital motion.

Magnetic Domain

Group of aligned magnetic dipoles.

Magnetic Permeability

Ability to attract magnetic field lines

Magnetic Susceptibility

How easily a material becomes magnetized

Natural Magnet

Gets magnetism from Earth (e.g., lodestone).

Artificial-Permanent Magnet

Man-made, retains magnetism (bar or horseshoe; e.g., compass).

Electromagnet

Coil around iron core producing intensified magnetic field.

Nonmagnetic

Not affected by magnetic fields (wood, glass).

Diamagnetic

Weakly repelled by both poles (copper, water, plastic).

Paramagnetic

Weakly attracted to both poles (gadolinium; MRI contrast).

Ferromagnetic

Strongly magnetized (AlNiCoFe).

Soft Iron

Excellent temporary magnet.

Like Poles Repel

Unlike Poles Attract

Opposite poles pull together.

South

Magnetic lines enter the _ pole.

North

Magnetic lines exit the pole.