Paper 2 physics

Isotope

Atoms of the same element with the same number of protons but different numbers of neutrons.

Nucleon

A particle in the nucleus: either a proton or a neutron.

Atomic Number (Z)

The number of protons in an atom's nucleus.

Mass Number (A)

The total number of protons and neutrons in an atom's nucleus.

Radioactive Decay

The spontaneous and random emission of radiation from an unstable nucleus.

Alpha Decay (α)

Emission of a helium nucleus (2 protons and 2 neutrons).

Beta Minus Decay (β⁻)

Neutron transforms into a proton, emitting an electron and an antineutrino.

Beta Plus Decay (β⁺)

Proton transforms into a neutron, emitting a positron and a neutrino.

Gamma Decay (γ)

Emission of a high-energy photon with no change in mass or atomic number.

Electron Capture

A proton in the nucleus captures an inner-shell electron and becomes a neutron.

Activity (A)

The number of nuclear decays per second, measured in becquerels (Bq).

Decay Constant (λ)

The probability per unit time that a nucleus will decay.

Half-Life (t₁/₂)

Time taken for half the radioactive nuclei in a sample to decay.

Random, Spontaneous Process

The unpredictable nature of individual nuclear decays, but statistically reliable over large numbers.

Mass Defect

The difference between the total mass of the separated nucleons and the mass of the nucleus.

Binding Energy

The energy required to break a nucleus into its component nucleons.

Binding Energy per Nucleon

The binding energy divided by the number of nucleons; indicates nuclear stability.

Nuclear Force

The strong, short-range attractive force that holds nucleons together.

Nuclear Instability

Occurs when a nucleus has an imbalance of neutrons and protons or is too massive.

Nuclear Fission

Splitting of a heavy nucleus into lighter nuclei, releasing energy and neutrons.

Nuclear Fusion

Joining of light nuclei to form a heavier nucleus, releasing energy.

Chain Reaction

A self-sustaining reaction where the products cause further reactions.

Critical Mass

The minimum amount of fissile material needed to maintain a chain reaction.

Q-Value

The net energy change in a nuclear reaction, calculated from mass difference.

Nuclear Radius

Proportional to A^(1/3); typical values are in femtometres (1 fm = 1 x 10^-15 m).

Nuclear Density

Approximately constant across all nuclei; much greater than atomic density.

Capacitance (C)

The charge stored per unit potential difference; C = Q / V.

Farad (F)

The SI unit of capacitance; 1 F = 1 coulomb per volt.

Dielectric

An insulating material placed between the plates of a capacitor to increase capacitance.

Relative Permittivity (εᵣ)

The ratio of the permittivity of a material to the permittivity of free space.

Time Constant (τ)

Product of resistance and capacitance; τ = RC. It represents the time for charge or voltage to fall to 1/e of its initial value.

Exponential Decay in Capacitors

Describes how voltage, current, or charge decrease over time in an RC circuit.

Energy Stored in a Capacitor

E = ½CV² or E = ½QV or E = ½Q²/C

Electric Field Strength (E)

The force per unit charge experienced by a small positive test charge; E = F / Q.

Uniform Electric Field

An electric field with constant magnitude and direction between two parallel plates.

Field Lines

Lines that show the direction of force on a positive test charge; denser lines indicate stronger fields.

Coulomb’s Law

The electrostatic force between two point charges is proportional to the product of the charges and inversely proportional to the square of the distance between them.

Permittivity of Free Space (ε₀)

A constant in Coulomb’s law, approx. 8.85 × 10⁻¹² F·m⁻¹.

Electric Potential (V)

The work done per unit charge to bring a charge from infinity to a point in the field.

Equipotential Lines

Lines or surfaces on which the electric potential is constant; no work is done moving along them.

Relationship Between E and V

E = −dV/dr for radial fields or E = V/d for uniform fields.

Capacitance of Parallel Plate Capacitor

C = ε₀εᵣA / d, where A is the area of plates and d is the separation.

Gravitational Field Strength (g)

The force per unit mass experienced by a mass in a gravitational field; g = F / m.

Newton’s Law of Gravitation

The gravitational force between two masses is proportional to the product of the masses and inversely proportional to the square of the distance between them.

Gravitational Potential (V)

The work done per unit mass to move a mass from infinity to a point in the field.

Equipotential Surfaces

Surfaces on which gravitational potential is constant; no work is done moving along them.

Radial Field

A field that radiates out from a central point; both gravitational and electric fields can be radial.

Gravitational Potential Energy (U)

U = -GMm/r for point masses.

Escape Velocity

The minimum velocity needed for an object to escape a gravitational field without further propulsion.

Magnetic Flux Density (B)

The strength of a magnetic field; B = F / (IL sinθ).

Tesla (T)

The SI unit of magnetic flux density; 1 T = 1 N·A⁻¹·m⁻¹.

Magnetic Force on a Current-Carrying Wire

F = BIL sinθ, where θ is the angle between field and current.

Magnetic Force on a Moving Charge

F = Bqv sinθ.

Magnetic Flux (Φ)

The product of magnetic flux density and area perpendicular to the field; Φ = BA.

Magnetic Flux Linkage

Product of flux and number of turns; NΦ.

Faraday’s Law

The induced emf is equal to the rate of change of magnetic flux linkage; emf = -d(NΦ)/dt.

Lenz’s Law

The direction of the induced emf is such that it opposes the change producing it.

Motor Effect

A current-carrying wire in a magnetic field experiences a force.

Electromagnetic Induction

The generation of an emf by changing magnetic flux.

Internal Energy

The total kinetic and potential energy of the particles in a substance.

Specific Heat Capacity (c)

The energy required to raise the temperature of 1 kg of a substance by 1°C or 1 K.

Specific Latent Heat (L)

The energy required to change the state of 1 kg of a substance without changing its temperature.

Ideal Gas

A gas that obeys the ideal gas law under all conditions of temperature and pressure.

Ideal Gas Equation

pV = nRT, where p = pressure, V = volume, n = number of moles, R = gas constant, and T = temperature.

Boltzmann Constant (k)

k = R / Nₐ, where R is the gas constant and Nₐ is Avogadro's number.

Kinetic Theory of Gases

Model that explains gas properties in terms of the motion of molecules.

Root Mean Square Speed (rms speed)

The square root of the mean of the squares of the speeds of particles in a gas.

Absolute Zero

The lowest possible temperature at which particles have minimum thermal motion (0 K).

Brownian Motion

Random motion of particles suspended in a fluid due to collisions with fast-moving molecules.