GRE · GRE Subject Test · GRE 物理 · 知识点 25
Measuring conductivity alone does not tell you whether electrons or holes dominate transport. A magnetic Hall measurement provides a sign-sensitive test.
Prerequisites: 8, 46.
| English | 中文 | 拼音 |
|---|---|---|
| binding energy per nucleon/ˈbaɪndɪŋ ˈenədʒi pɜː ˈnjuːklɪən/ | 平均核子结合能 | píng jūn hé zǐ jié hé néng |
Binding energy B is the energy needed to separate a nucleus into its constituent free nucleons, equal to the corresponding mass deficit times c². Binding energy per nucleon B/A is the relevant comparison across different mass numbers; a heavier nucleus can have greater total B but lower B/A. The broad B/A maximum is near the iron/nickel region. Light-nucleus fusion and very-heavy-nucleus fission can release energy when products have greater total binding. For a reaction, Q=(initial rest mass−final rest mass)c²; positive Q means released energy. Always compare the actual specified isotopes and final products, not just their element names.
Leptons such as electrons, muons and neutrinos are not made of constituent quarks in the Standard Model. A negative muon has charge −e and spin 1/2, like an electron, but has a different mass and belongs to a different flavour family; it is not a meson despite its historical name. Hadrons contain quarks: ordinary mesons have one quark and one antiquark, and ordinary baryons have three quarks. Corresponding antibaryons have three antiquarks. These elementary classification models do not imply every composite particle is a simple baryon or meson.
Check charge, energy, momentum, baryon number and relevant lepton numbers in a proposed process. A proton’s uud quarks sum to charge +e; neutron udd sums to zero. Beta-minus decay n→p+e−+antineutrino conserves electric charge and includes the antineutrino to balance lepton number and kinematics. A particle’s mass alone does not classify it as a quark, lepton or hadron. Reaction thresholds may require kinetic energy beyond an exothermic rest-mass difference when other constraints apply.
In a simple one-carrier conductor, transverse magnetic Lorentz force builds a Hall electric field until transverse carrier force balances. With a stated tensor/sign convention, Hall coefficient 霍尔系数 is R_H=1/(nq); negative q gives electron-like negative coefficient, positive q gives hole-like positive coefficient. Resistivity magnitude alone does not reveal this sign. Set current, magnetic field and voltage directions consistently before reading raw polarity. Semiconductors with electrons and holes both contributing require a mobility-weighted two-carrier model; the simple coefficient need not equal the inverse total carrier density.
| English | 中文 | 拼音 |
|---|---|---|
| Hall coefficient/hɔːl ˌkəʊɪˈfɪʃənt/ | 霍尔系数 | huò ěr xì shù |
In a one-carrier Hall effect 霍尔效应 model, use $R_H=1/(nq)$ with a fixed lead convention. For electrons, q = -e, n = $5.0\times10^{22}$ per cubic metre,
| English | 中文 | 拼音 |
|---|---|---|
| Hall effect/hɔːl ɪˈfekt/ | 霍尔效应 | huò ěr xiào yìng |
Compare binding per nucleon, not just total binding. A muon is a lepton, and Hall sign requires the declared measurement convention and carrier model.
binding energy per nucleon: Nuclear binding energy divided by nucleon count.
Hall coefficient: Signed proportionality relating transverse Hall field to current density and magnetic field under a stated convention.
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