Ch 18: Electric Charge and Electric Field

Vocabulary flashcards covering key terms and concepts from Chapter 18: Electric Charge and Electric Field.

Coulomb's Law

Describes the force between two point charges: F = k|q1 q2|/r^2; repulsive for like charges, attractive for opposite; directed along the line joining the charges.

Electric charge

Property of matter that causes electric forces; two types (positive and negative); quantized in units of the elementary charge e.

Insulators

Materials that resist the flow of electric charge; electrons are tightly bound; can be polarized.

Conductors

Materials with freely moving electrons; charges reside on the surface at electrostatic equilibrium.

Semiconductors

Materials with conductivity between conductors and insulators; controlled by doping and temperature.

Grounding

Connection to Earth that allows excess charge to flow to/from ground, enabling charge redistribution.

Charging by Conduction

Direct transfer of electrons when objects touch until electrical equilibrium is reached.

Charging by Induction

Redistribution of charges in a conductor due to a nearby external charge, often with grounding; total charge is conserved.

Polarization

Temporary separation of charges within a neutral object in an external electric field; induced dipoles; field inside conductor cancels.

Electric field (E)

Region where a test charge experiences a force; E = F/q; direction depends on source charges; lines point away from positive charges and toward negative.

Field lines

Visual representation of the electric field; density indicates strength; lines do not cross; show direction of force on a positive test charge.

Superposition principle (electric field)

The net electric field is the vector sum of the fields from all charges.

Electric field of a point charge

E = k|q|/r^2; directed radially; away from positive charges, toward negative charges.

Charge quantization

Elementary charge e = 1.602×10^-19 C; smallest unit of electric charge carried by particles.

Electron

Subatomic particle with charge -e and mass 9.11×10^-31 kg; forms a negative cloud around the nucleus.

Proton

Subatomic particle with charge +e and mass 1.67×10^-27 kg; located in the nucleus.

Neutron

Electrically neutral subatomic particle in the nucleus.

Free electrons

Electrons not bound to atoms; in metals form a 'sea' that moves in response to electric fields; number density affects conductivity.

Surface charge

In conductors at electrostatic equilibrium, excess charges reside on the outer surface.

Electric field units

Units: N/C or V/m; both describe field intensity.

Inverse-square law

Force ∝ 1/r^2; doubling distance reduces force by factor of 4; electric forces are strong at atomic scales.

Vector nature of E

Electric field is a vector with magnitude and direction; adds via vector addition.

Electric field due to multiple charges

Use the superposition principle: Enet = E1 + E2 + …; combine components.

Faraday cage

Conducting enclosure that shields its interior from external static electric fields.

Corona discharge

Discharge caused by high electric field around sharp conductors, ionizing surrounding air when dielectric strength is exceeded.

Lightning rod

Sharp conductor that concentrates the field to provide a preferred safe discharge path for lightning.

Surface charge density and field focus

Field is strongest near sharp points or edges due to charge concentration; geometry affects local field strength.

Shielding

Reduction of electric field effects inside a conductor; outside fields influence surface charges to cancel interior field.

Gauss's law (conceptual)

Relation between electric flux through a closed surface and enclosed charge; explains field behavior in symmetric situations.

Charge conservation

Total electric charge in an isolated system remains constant; charges can be transferred but not created/destroyed.