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Showing 1561–1590 of 1709 reference entries

PhysicsSimple harmonic motion and period

Linear restoring acceleration produces sinusoidal motion.

ModelPhysicsSimple pendulum and the small-angle limit

The familiar pendulum period requires a small swing.

ModelPhysicsAmplitude, phase, wavelength and polarization direction

A wave’s pattern speed differs from the motion of its medium.

ModelPhysicsEnergy carried by a sinusoidal string wave

Energy transport grows with squared amplitude and frequency in the linear model.

ModelPhysicsSound intensity and decibel level

A decibel value needs a reference and a specified measured quantity.

ModelPhysicsBeats from nearby frequencies

Slow modulation comes from superposing close frequencies.

ModelPhysicsAcoustic Doppler shift in a medium

Source and observer velocities are measured relative to the medium.

ModelPhysics · ChemistryHeat, temperature and specific heat

Heat is energy transferred because of a temperature difference.

ModelPhysicsThermal expansion coefficients

Thermal size changes depend on temperature and constraints.

ModelPhysics · ChemistryPressure–volume work and process paths

Boundary work depends on the process, while internal energy is a state function.

ModelPhysics · ChemistryReversible adiabatic ideal-gas relations

The power law needs an ideal gas and constant heat-capacity ratio.

ModelPhysics · ChemistryReversible and quasistatic processes

Restoring the system alone does not establish reversibility.

ModelPhysics · ChemistryEntropy change and reversible heat transfer

Use a reversible comparison path to calculate a state-function change.

ModelPhysicsRefrigerator and heat-pump performance

A heat pump moves heat as well as consuming work.

ModelPhysics · ChemistryMean free path in a dilute hard-sphere gas

A collision length depends on number density and cross section.

ModelPhysicsAtomic net charge and electrical neutrality

Neutral matter can contain both positive and negative charge.

ModelPhysicsConductors, insulators and electrostatic induction

Charge mobility and polarization are different from net charging.

ModelPhysicsConductors in electrostatic equilibrium

Equilibrium field vanishes in the conducting material, including a charged conductor.

ModelPhysicsElectric potential, voltage and potential energy

Voltage is energy change per unit charge.

ModelPhysicsCurrent density and carrier drift

Current measures signed charge flow across a surface.

ModelPhysicsResistance, resistivity and conductor geometry

Resistance belongs to a device geometry; resistivity is a material response.

ModelPhysicsSeries and parallel resistor networks

Series shares current; parallel shares voltage.

ModelPhysicsElectrical power and Joule heating

Voltage times signed current measures element power.

ModelPhysicsElectromotive force and terminal voltage

An emf is an energy-per-charge quantity, not a force.

ModelPhysicsSeries and parallel capacitor networks

Capacitor network rules differ from resistor rules.

ModelPhysicsEnergy stored in a linear capacitor

Charging work produces electric-field energy.

ModelPhysicsMagnetic flux and Faraday–Lenz induction

Induction responds to flux change, not simply to the presence of a magnetic field.

ModelPhysicsEnergy stored in a linear inductor

Inductive storage and resistive loss are separate.

ModelPhysicsMagnetic fields of a straight wire and circular loop

Field geometry follows the current distribution.

ModelPhysicsIdeal transformer voltage and current ratios

Turns change voltage and current while conserving ideal power.

Model
ModelSource checked

Electromotive force and terminal voltage

Physics

An emf is an energy-per-charge quantity, not a force.

Key knowledge

A source emf measures supplied work per unit charge and has units of volts. An ideal emf source with a series internal resistance r models a discharging battery’s terminal voltage as V_terminal=ε−Ir, where I leaves its positive terminal. At zero current this model gives V_terminal=ε; under load internal dissipation lowers terminal voltage.

Values and equations

ε=dW_source/dq; V_terminal=ε−Ir

ε,V_terminal
Source emf and terminal voltage V
W_source
Work supplied by source mechanisms J
q
Transported charge in the stated source orientation C
I
Current leaving the positive terminal during discharge A
r
Series internal resistance Ω

Conditions and scope

  • Quasistatic two-terminal source model with a stated emf and linear internal resistance r≥0 over the operating range.
  • Charging reverses the current sign and can make terminal voltage exceed emf. Real electrochemical sources have state, temperature, history and rate dependence; the simple model does not make r a universal constant.
Sources · 1

References

Sources retain their recorded scope. A source link alone does not establish verification of every statement.

  1. University Physics Volume 2, §10.1: electromotive forceSamuel J. Ling, Jeff Sanny and William Moebs — OpenStax, Rice University, University Physics (2016)Textbook chapteropenstax.orgRead source

Evidence and review

Read §10.1 emf work-per-charge definition and Internal Resistance and Terminal Voltage10.2. Exclude the source’s blanket “terminal voltage is always less” claim; the discharge sign is explicit.

2026-10-10 · /root/audit_life_earth_chemistry — independent Chemistry/Life/Earth editor. Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.

Related reference entries

Explore relationships within this area of study and its connections to other areas.

Showing 1–4 of 4 relationships

Scientific relationships · 4 / 4

The relationship type describes the connection. Its linked statements, sources and conditions define the scope.

  1. Uses definition
    Relationship sources · 1

    Linked statements

    • A source emf measures supplied work per unit charge and has units of volts. An ideal emf source with a series internal resistance r models a discharging battery’s terminal voltage as V_terminal=ε−Ir, where I leaves its positive terminal. At zero current this model gives V_terminal=ε; under load internal dissipation lowers terminal voltage.

    This relation concerns the stated electromotive force and terminal voltage claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.

  2. Uses definition
    Relationship sources · 1

    Linked statements

    • A source emf measures supplied work per unit charge and has units of volts. An ideal emf source with a series internal resistance r models a discharging battery’s terminal voltage as V_terminal=ε−Ir, where I leaves its positive terminal. At zero current this model gives V_terminal=ε; under load internal dissipation lowers terminal voltage.

    This relation concerns the stated electromotive force and terminal voltage claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.

  3. Uses definition
    Relationship sources · 1

    Linked statements

    • A source emf measures supplied work per unit charge and has units of volts. An ideal emf source with a series internal resistance r models a discharging battery’s terminal voltage as V_terminal=ε−Ir, where I leaves its positive terminal. At zero current this model gives V_terminal=ε; under load internal dissipation lowers terminal voltage.

    This relation concerns the stated electromotive force and terminal voltage claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.

  4. Uses definition
    Relationship sources · 2

    Linked statements

    • Magnetic flux through an oriented surface is Φ_B=∫B·n dA. For a fixed conducting loop, Faraday’s law gives induced electric emf ∮E·dl=−dΦ_B/dt with surface and boundary orientations related by the right-hand rule. N identical fixed turns linking the same flux give ε=−N dΦ_B/dt. The minus sign sets the circulation; any resulting current depends on the circuit response.

    This relation concerns the stated magnetic flux and faraday–lenz induction claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.

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