A2 Physics Definitions, terms and laws

radian

angle subtended at centre of a circle when arc length is equal to the radius

gravitational field (strength at a point)

force per unit mass

gravitational potential at a point

work done per unit mass in bringing a small test mass from infinity to the point

specific heat capacity

thermal energy per unit mass per unit change in temperature

specific latent heat

thermal energy per unit mass to change state at constant temperature

specific latent heat of fusion

specific latent heat of vaporisation

electric field (at a point)

force per unit positive charge

electric potential at a point

work done per unit positive charge in bringing a small test charge from infinity to the point

capacitance of a parallel‑plate capacitor

charge per unit potential (difference) where charge is on one plate, and potential difference is between the plates

magnetic flux density

force acting per unit current per unit length on a wire placed at perpendicular to the magnetic field

magnetic flux

product of the magnetic flux density and the cross-sectional area perpendicular to the direction of the magnetic flux density

mass defect of a nucleus

difference between mass of nucleus and mass of constituent nucleons when nucleons are separated to infinity

binding energy (of a nucleus)

minimum energy required to separate the nucleons of a nucleus to infinity

activity of a radioactive sample

number of nuclear disintegrations per unit time

decay constant

probability of decay (of a nucleus) per unit time

half-life

time for activity to halve

specific acoustic impedance (of a medium)

the product of density and speed of the sound in the medium

basic assumptions of the kinetic theory of gases (5)

• molecules are in continuous random motion

• molecules have negligible volume compared with volume of gas

• no forces exerted between the molecules of the gas except during collisions

• collisions (involving molecules) are (perfectly) elastic

• collisions (of molecules) are instantaneous

internal energy

sum of potential energy and kinetic energy of random motion of particles in a system

Newton’s law of gravitation

gravitational force is directly proportional to product of masses where the force between point masses is inversely proportional to the square of their separation

two objects being in thermal equilibrium

the two objects are at the same temperature where there is no net transfer of thermal energy between them

first law of thermodynamics

the change in internal energy is the sum of work done and energy transfer by heating and so an increase in internal energy is equal to the sum of work done on system and energy transferred to the system by heating

damping

loss of energy of oscillations due to resistive forces

contrast in an X-ray image

difference in degrees of blackening

uniform circular motion of an object

velocity and acceleration both have constant magnitude where velocity is perpendicular to acceleration

Faraday’s law of electromagnetic induction

induced e.m.f. is directly proportional to rate of change of magnetic flux linkage

Lenz’s law of electromagnetic induction

direction of (induced) e.m.f. is such as to (produce effects that) oppose the change that caused it

photon

packet / quantum of energy of electromagnetic radiation

Wien’s displacement law

temperature inversely proportional to wavelength where temperature is thermodynamic temperature of surface of star and wavelength is the wavelength at which maximum emission rate from star occurs

Coulomb’s law

electric force is directly proportional to product of charges where the force between point charges is inversely proportional to the square of their separation

rectification

conversion from a.c. to d.c.

de Broglie wavelength

wavelength associated with a moving particle

Hubble’s law

speed is directly proportional to distance where the speed is of recession of galaxy from an observer, and distance is the distance of the galaxy from the observer

gravitational field line

direction of force acting on a test mass

Electric field line

Direction of force acting on a positive charge

simple harmonic motion

motion in which acceleration is directly proportional to displacement motion in which acceleration is in the opposite direction to displacement

photoelectric effect

emission of electrons from a metal surface when electromagnetic radiation is incident on surface / electrons

spontaneous

decay is not affected by external / environmental factors

random

cannot predict when a nucleus will decay

luminosity of a star

total power of radiation emitted by the star

threshold wavelength

maximum wavelength (of electromagnetic radiation) that causes electrons to be emitted (from surface of metal)

frequency of an alternating current

number of cycles per unit time

Avogadro constant

number of particles per unit amount of substance

ideal gas

gas for which pV is directly proportional to T where T is thermodynamic temperature

resonance

oscillation of object at maximum amplitude when driving frequency is equal to the natural frequency of system

tesla

newton per ampere where the wire is perpendicular to the magnetic field

field of a force

region (of space) where a particle experiences a force

radioactive

unstable nucleus emits ionising radiation or decays spontaneously

tracer

substance containing radioactive nuclei that is introduced into the body

annihilation

a particle interacting with its antiparticle so that mass is converted into energy