Physics: Forces and Fields (Unit B)

Comprehensive vocabulary flashcards reviewing the key terms, laws, and concepts from Physics Unit B: Forces and Fields, including electrostatics, Coulomb's law, electric and magnetic fields, potential difference, Millikan's experiment, and electromagnetic induction.

Electrostatics

The study of electric charges that can be collected and held in one place.

Law of Conservation of Charge

A fundamental physics principle stating that the total charge of an isolated system remains constant; the sum of the charges before an interaction equals the sum of the charges after the interaction.

Charging by Friction

The process of separating electrons from atoms in one object through rubbing and transferring and depositing them onto the atoms of another object.

Charging by Conduction

The transfer of electrons from a charged object to an uncharged object by direct physical contact.

Charging by Induction

The redistribution or shift of charges within a neutral object caused by the proximity of an external charged object without direct contact.

Triboelectric Series

A ranking of materials used to determine whether an object will become positively or negatively charged after being rubbed with another material.

Conductor

A material that allows electrical charges to move about easily.

Insulator

A material through which an electric charge will not move easily.

Semiconductor

A material that behaves as a good conductor under certain conditions and as a good insulator under other conditions.

Superconductor

A material that exhibits no measurable electrical resistance when cooled to very low temperatures.

Coulomb's Law

A law stating that the electrostatic force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them: $|\vec{F}_e| = \frac{k q_1 q_2}{r^2}$.

Coulomb's Law Constant ($k$)

The electrostatic proportionality constant, equal to $8.99 \times 10^9\,\text{N}\cdot\text{m}^2/\text{C}^2$.

Coulomb's Torsion Balance

An apparatus used to verify Coulomb's law by measuring the angle of twist produced in a suspended fiber by the electrostatic force between two charged spheres.

Field

A region of influence surrounding an object.

Electric Field ($\vec{E}$)

A vector field representing the electrostatic force per unit charge ($\vec{E} = \frac{\vec{F}_e}{q}$), with the direction defined as the direction of the force exerted on a positive test charge.

Electric Field Lines

Lines of force drawn radially away from positive charges and radially toward negative charges, where the spacing density of the lines indicates field intensity.

Electric Potential Difference ($\Delta V$)

The change in electric potential energy per unit of charge ($\Delta V = \frac{\Delta E}{q}$), also known as voltage.

Electron Volt ($\text{eV}$)

A unit of energy equal to the change in potential energy experienced by an electron moving across a potential difference of $1\,\text{V}$, equivalent to $1.60 \times 10^{-19}\,\text{J}$.

Equipotential Lines

Lines connecting points in an electric field between which the electric potential difference is zero; they always cross electric field lines perpendicularly at $90^\circ$.

Electric Current ($I$)

The quantity of charge passing a reference point in a conductor per unit of time ($I = \frac{q}{t}$), measured in amperes ($\text{A}$).

Millikan's Oil-Drop Experiment

An experiment that determined the elementary unit of electric charge by balancing the downward gravitational force with the upward electric force ($F_e = F_g$) on charged oil droplets suspended between parallel plates.

Charge Quantization

The principle that electric charge is not continuous but exists only in discrete integer multiples of a fundamental unit of charge.

Elementary Unit of Charge ($e$)

The fundamental quantum of electric charge carried by a single proton or electron, equal to $1.60 \times 10^{-19}\,\text{C}$.

Law of Magnetism

The physical law stating that like magnetic poles repel each other, while unlike magnetic poles attract each other.

Magnetic Field

A three-dimensional vector field surrounding a magnet or moving charge, with field lines drawn exiting the north pole and entering the south pole.

Magnetic Domains

Microscopic regions within a ferromagnetic material (typically $0.001\,\text{mm}$ to $1\,\text{mm}$ in size) where the magnetic fields of constituent atoms are mutually aligned.

Ferromagnetic Substances

Materials such as iron, cobalt, and nickel (MagNiFeCo) whose magnetic domains can align in the presence of an external magnetic field to become magnetized.

Oersted's Discovery

The discovery by Hans Christian Oersted that an electric current flowing through a wire creates a magnetic field that deflects a compass needle.

First Left-Hand Rule

A rule determining the magnetic field around a straight conductor carrying electron flow: the left thumb points in the direction of electron flow, while the curled fingers point in the direction of the circular magnetic field lines.

Solenoid

A cylindrical coil of conducting wire that generates an internal and external magnetic field resembling that of a bar magnet when an electric current flows through its loops.

Second Left-Hand Rule

A rule determining the polarity of an electromagnet or solenoid: when the fingers of the left hand curl around the loops in the direction of electron flow, the outstretched thumb points toward the north pole.

Cathode Ray

A stream of high-speed electrons emitted from a negative cathode and accelerated toward an anode in an evacuated glass tube.

Third Left-Hand Rule

A hand rule used to find the magnetic force on moving electrons: the thumb points in the direction of electron velocity, extended fingers point in the direction of the external magnetic field, and the palm points in the direction of the deflecting magnetic force.

Magnetic Deflecting Force on a Moving Charge ($|\vec{F}_m|$)

The magnetic force exerted on a moving charged particle, given by $|\vec{F}_m| = q v_\perp |\vec{B}|$, where $v_\perp = v \sin(\theta)$.

Magnetic Force on a Current-Carrying Conductor

The magnetic force exerted on a length of wire carrying electric current in an external magnetic field, calculated as $|\vec{F}_m| = I l_\perp |\vec{B}|$.

Mass Spectrometer

An analytical instrument that uses electric fields to accelerate ions and magnetic fields to deflect them along circular paths ($F_m = F_c$) in order to separate and measure their masses.

Electromagnetic Induction

The production of an electric current or potential difference (emf) across a conductor when it cuts through magnetic field lines or experiences a changing magnetic flux.

Lenz's Law

A principle of electromagnetic induction stating that the direction of an induced current is always such that its own magnetic field opposes the change in magnetic flux that caused it.