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Showing 61–90 of 1709 reference entries

Physics · MeasurementElectric current

Current measures charge crossing a chosen surface per unit time.

DefinitionPhysicsElectric field and force

An electric field assigns force per unit test charge.

DefinitionPhysicsMagnetic force on a moving charge

Magnetic force depends on charge motion relative to the field.

ModelPhysicsOhm's law and its domain

A linear current-voltage relation requires suitable conditions.

Empirical findingPhysicsFirst law of thermodynamics

Keep the heat and work sign convention explicit in an energy balance.

ModelPhysicsSecond law: isolated-system entropy

Apply entropy increase to the whole isolated system.

ModelPhysics · ChemistryIdeal-gas equation of state

A simple gas model relates pressure, amount, volume and temperature.

ModelPhysicsPhoton energy and frequency

One photon's energy is proportional to its frequency.

ModelPhysics · Mathematics & logicInvariant spacetime interval

Lorentz transformations preserve a combined space-time separation.

ModelPhysicsNewton's third law

Interaction forces act on different bodies in equal and opposite pairs.

ModelPhysicsAngular momentum and torque

Torque changes angular momentum about a specified origin.

ModelPhysicsHydrostatic pressure

Static fluid pressure rises with depth under gravity.

ModelPhysicsArchimedes' buoyancy principle

The hydrostatic upward force equals displaced-fluid weight.

ModelPhysicsMaxwell equations in free space

Four field equations connect electric and magnetic fields with charge and current.

ModelPhysicsSchrödinger time evolution

A quantum wavefunction evolves according to its Hamiltonian.

ModelPhysicsBorn position probability

A normalized wavefunction assigns probabilities to position intervals.

ModelPhysics · MeasurementElementary charge

The elementary charge has an exact SI numerical value.

DefinitionPhysics · MeasurementBoltzmann constant

The Boltzmann constant has an exact SI numerical value.

DefinitionMeasurement · Chemistry · PhysicsAvogadro constant

The mole is linked to a specified number of entities.

DefinitionMeasurement · PhysicsSI defining luminous efficacy

A specified frequency fixes the photometric SI reference.

DefinitionChemistryAtoms and elemental identity

The proton count of an atomic nucleus identifies its chemical element.

DefinitionChemistryIsotopes and mass number

Isotopes share a proton count but have different neutron counts.

DefinitionChemistryPeriodic organization of the elements

Atomic-number order reveals recurring patterns in electron structure and chemical properties.

ModelChemistryChemical bonds

Bonding describes interactions that bind atoms into molecules or extended structures.

DefinitionChemistry · MeasurementMole and amount of substance

The mole counts specified entities using the exact Avogadro constant.

DefinitionChemistryReaction stoichiometry

Balanced coefficients relate the amounts consumed and produced by a reaction.

MethodChemistryBalancing atoms and electric charge

A chemical equation must preserve each element's atom count and the total charge.

MethodChemistryDynamic chemical equilibrium

At equilibrium, opposing reactions continue without net composition change.

ModelChemistryBrønsted acids and bases

In the Brønsted description, an acid donates a proton and a base accepts it.

DefinitionChemistryGibbs energy and thermodynamic direction

Gibbs-energy change distinguishes thermodynamic favourability from reaction speed.

Model
ModelSource checked

First law of thermodynamics

Physics

Keep the heat and work sign convention explicit in an energy balance.

Key knowledge

For a closed thermodynamic system, with changes of bulk kinetic and gravitational potential energy neglected, the internal-energy change is ΔU = Q − W: Q is heat entering the system and W is work done by it.

Values and equations

ΔU = Q − W

ΔU
Change in internal energy J
Q
Heat transferred into the system J
W
Work done by the system J

Conditions and scope

  • No matter crosses the boundary; include all relevant forms of work.
  • The stated sign convention applies; other conventions reverse the work term.
  • Use equilibrium end states to assign U in this introductory balance.
Sources · 3

References

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

  1. University Physics Volume 2, 3.3 First Law of ThermodynamicsSamuel J. Ling, William Moebs and Jeff Sanny — OpenStax / Rice UniversityTextbook chapteropenstax.orgRead source
  2. First Law — Internal EnergyNASA Glenn Research CenterTeaching resourcewww1.grc.nasa.govRead source
  3. Thermodynamics · Physics (2026–27 reprint)National Council of Educational Research and Training (NCERT)Textbook chapter · PDFncert.nic.inRead source

Evidence and review

OpenStax 3.3, equation 3.7 and sign table; NASA state-to-state Q-in/W-out balance.

2026-10-10 · Closed-system internal-energy balance under stated simplifications only; flowing matter and changing bulk motion need additional energy terms.

Foundational review

2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.

Sources from other places

Agreement within this scope

With work done by a closed system positive, heat input minus work output changes internal energy when bulk-energy changes are excluded.

Changing the work sign convention changes the equation’s sign, not the energy balance.

Related reference entries

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

Showing 1–12 of 12 relationships

Scientific relationships · 12 / 12

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

  1. Uses definition
    Relationship sources · 1

    Heat and work cross the specified closed-system boundary under the adopted sign convention.

  2. Related to
    Relationship sources · 1

    Linked statements

    • In one-dimensional isotropic local conduction, heat flux q_x = −κ dT/dx. Positive conductivity κ makes flux point toward decreasing temperature.

    Conductive heat transfer supplies a term in a specified energy balance; the local transport law is additional modeling.

  3. Related to
    Relationship sources · 3

    Linked statements

    • For mass m undergoing a specified equilibrium transition at fixed pressure, the latent heat magnitude is Q = mℓ. Fusion and vaporization absorb heat; their reverse transitions release it.

    For a closed system with negligible bulk kinetic/gravitational potential energy changes, a mechanically quasistatic constant-pressure transition with only pressure–volume work has heat equal to its enthalpy change.

  4. Related to
    Relationship sources · 1

    Linked statements

    • For a specified nucleus, binding energy B = [Z m_p + (A−Z)m_n − m_nucleus]c² is the energy needed to separate it into free protons and neutrons.

    Rest-energy release and supplied dissociation energy use consistent total-energy accounting; not the nonrelativistic heat/work formula alone.

  5. Related to
    Relationship sources · 2

    Linked statements

    • For a simple compressible equilibrium system, U(S,V,{N_i}) has differential dU=T dS−p dV+Σ_i μ_i dN_i. Temperature, pressure and chemical potentials are the corresponding partial derivatives of U; particle-number changes are distinct from heat transfer.

    An equilibrium extensive-state differential identifies temperature, pressure and composition work; actual irreversible paths need separate entropy accounting.

  6. Related to
    Relationship sources · 1

    Linked statements

    • In a constant-density,constant-heat-capacity incompressible sensible-heat model, ρ₀c_pDT/Dt=−∇·J_H+q_H. J_H is nonadvective heat flux directed toward heat transport and q_H volumetric heat addition. A control volume gains thermal energy by net inward advective/nonadvective flux and internal sources. Density/compressibility and pressure-work corrections matter outside this bounded model.

    The thermal inventory balances specified heat transfer and sources.

  7. Related to
    Relationship sources · 2

    Linked statements

    • In a quasistatic elastic fracture model, crack extension releases mechanical potential energy at rateG=−∂Π/∂A per projected crack area. Extension becomes energetically possible whenG reaches the applicable resistanceG_c. For ideally brittle creation of two clean surfaces with surface energyγ each,G_c=2γ; real process-zone dissipation can raise the resistance. Flaw geometry and size therefore matter alongside remote stress.

    Released energy has multiple storage/dissipation pathways.

  8. Related to
    Relationship sources · 1

    Linked statements

    • Heat names energy transfer caused by a temperature difference, rather than a substance stored in an object. Temperature and internal energy are different state quantities. For a fixed mass heated along a specified process without a phase transition, Q=m∫c(T)dT; if the process-specific c is nearly constant, Q≈mcΔT. Pressure and volume constraints can give different specific heats.

    The two records describe related physical or metrological models or distinctions; the present claim does not require every hypothesis or result in the linked record.

  9. Uses definition
    Relationship sources · 2

    Linked statements

    • For a mechanically quasistatic simple compressible closed system, work done by the system is W=∫p dV: expansion contributes positive work and compression negative work. A quasistatic isothermal ideal gas with fixed amount gives W=nRTln(V_f/V_i). Isochoric means constant volume; isobaric constant pressure; isothermal constant temperature; adiabatic means no heat transfer.

    This relation concerns the stated pressure–volume work and process paths claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.

  10. Uses definition
    Relationship sources · 2

    Linked statements

    • For a cyclic device extracting heat Q_c>0 from a cold reservoir and delivering Q_h to a hot one with work input W>0, Q_h=Q_c+W. Refrigerator coefficient of performance is Q_c/W; heat-pump coefficient is Q_h/W=COP_R+1. For two reservoirs with T_h>T_c>0, reversible limits are T_c/(T_h−T_c) and T_h/(T_h−T_c). A coefficient above one does not create energy.

    This relation concerns the stated refrigerator and heat-pump performance claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.

  11. Related to
    Relationship sources · 3

    Linked statements

    • An open thermodynamic system permits matter to cross its boundary; a closed system permits no matter transfer but may exchange energy. An isolated system exchanges neither matter nor energy. Adiabatic means no heat transfer during the process: work can still transfer energy, so an adiabatic closed system need not be isolated.

    The first-law closed-system record allows heat and work transfers; the present entry distinguishes that boundary from isolation.

  12. Related to
    Relationship sources · 1

    Linked statements

    • A convective surface model relates outward heat flux to the surface-to-fluid temperature difference: q_out=h(T_s−T_∞). For uniform h and temperatures over area A, the outward heat-transfer rate is Q̇_out=hA(T_s−T_∞). The coefficient depends on the fluid, geometry and flow conditions; it is not just a fixed material property.

    A convective rate supplies a heat-transfer term in a suitable energy balance; it is not the complete first law.

Entry detailsPermanent link to this entry ↗
Record identity
physics-first-law-thermodynamics
Revision
core.1
Structured reference record
Essential core · first collection · University core expansion