Physics Definitions

its definitions for physics

Define the radian.

the angle subtended at the centre of a circle by an arc equal in length to the radius

State what is meant by angular speed.

the rate of change of angular displacement.

Explain what is meant by centripetal acceleration.

The acceleration of an object moving in a circular path, directed towards the center of the circle always perpendicular to the velocity.

Define gravitational field strength.

the force per unit mass

Define gravitational potential at a point.

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

State the conditions necessary for a body to execute simple harmonic motion.

acceleration must be proportional to displacement from a fixed point and always directed opposite to the displacement

State what is meant by the amplitude of an oscillation.

the maximum displacement from the equilibrium position

State what is meant by the period of an oscillation.

the time taken for one complete oscillation

State what is meant by the frequency of an oscillation.

the number of complete oscillations per unit time

State what is meant by the phase difference between two oscillations.

the fraction of a cycle or the angle by which one oscillation leads or lags another

State what is meant by light damping.

damping in which the amplitude decreases gradually over many cycles while the system keeps oscillating close to its natural frequency

State what is meant by critical damping.

the minimum amount of damping needed to return a displaced system to equilibrium in the shortest possible time without oscillating

State what is meant by heavy damping.

damping strong enough that a displaced system returns slowly to equilibrium without oscillating

State what is meant by resonance.

a maximum amplitude that occurs during oscillation when a system is forced to oscillate at its natural frequency

State what is meant by a photon.

a quantum of electromagnetic energy

State what is meant by the threshold frequency in the photoelectric effect.

the minimum frequency of electromagnetic radiation that can cause photoelectric emission from a given metal surface

State what is meant by the threshold wavelength in the photoelectric effect.

the maximum wavelength of electromagnetic radiation that causes photoelectric emission from the surface of a metal

State what is meant by the work function energy of a metal.

the minimum energy needed to remove an electron from the surface of the metal

State what is meant by the de Broglie wavelength of a particle.

the wavelength associated with a moving particle

Define the specific acoustic impedance of a medium.

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

State what is meant by a tracer, as used in medical imaging.

a substance containing radioactive nuclei that is introduced into the body and absorbed by the tissue being studied

State what is meant by annihilation.

a process in which a particle and its antiparticle interact so that their mass and energy are converted into photon energy, with momentum conserved

Define the term mass defect.

the difference between the total mass of the separate nucleons and the mass of the nucleus they form

Define the term binding energy of a nucleus.

the energy needed to completely separate a nucleus into its individual protons and neutrons

Define the activity of a radioactive source.

the number of nuclear decays occurring per unit time in a sample

Define the decay constant.

the probability that an individual nucleus will decay per unit time

Define the term half life.

the time taken for the number of undecayed nuclei, or the activity, of an isotope to fall to half its original value

Explain what is meant by nuclear fusion.

two light nuclei join together to form a heavier more stable nucleus while releasing energy

Explain what is meant by nuclear fission.

the splitting of a heavy unstable nucleus into two lighter nuclei with the release of energy

State what is meant by thermal equilibrium.

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

State what is meant by absolute zero.

the lowest possible temperature, zero kelvin, at which a substance has minimum internal energy

State what is meant by the internal energy of a system.

the sum of the random distribution of kinetic and potential energies of the particles in the system

State the first law of thermodynamics.

the increase in internal energy of a system equals the energy transferred to it by heating plus the work done on it

Define specific heat capacity.

the energy required per unit mass to raise the temperature of a substance by one degree without a change of state

Define specific latent heat.

the energy required per unit mass to change the state of a substance without a change in temperature

State what is meant by the specific latent heat of fusion.

the energy required per unit mass to change a substance from solid to liquid without a change in temperature

State what is meant by the specific latent heat of vaporisation.

the energy required per unit mass to change a substance from liquid to gas without a change in temperature

State what is meant by one mole of a substance.

the amount of substance that contains a number of particles equal to the Avogadro constant

State what is meant by an ideal gas.

a gas for which pressure times volume is proportional to thermodynamic temperature

Define electric field strength.

the force per unit positive charge

Define electric potential at a point.

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

Define capacitance.

the charge stored per unit potential difference across a capacitor

State what is meant by the luminosity of a star.

the total power of radiation emitted by the star

State what is meant by a standard candle.

an astronomical object of known luminosity that can be used to determine distances to galaxies

State Wiens displacement law.

wavelength of maximum intensity is inversely proportional to thermodynamic temperature

State Hubbles law.

the recession velocity of a distant galaxy is approximately proportional to its distance from us

Explain what is meant by the redshift of light from a distant galaxy.

the observed wavelength is greater than the known rest wavelength this is due to the star or galaxy moving away from the observer

Define magnetic flux density.

the force acting per unit current per unit length on a current carrying wire placed at right angles to the magnetic field

Define magnetic flux.

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

State what is meant by magnetic flux linkage.

the product of the magnetic flux through a coil and the number of turns on the coil

State Faradays law of electromagnetic induction.

the induced electromotive force is proportional to the rate of change of magnetic flux linkage

State Lenzs law.

the direction of an induced electromotive force is always such that it opposes the change producing it

State what is meant by the peak value of an alternating current or voltage.

the maximum value reached by the current or voltage during a cycle

Define the root mean square value of an alternating current.

the value of a direct current that would produce the same average power in a resistor as the alternating current

Explain what is meant by half wave rectification.

a process using a single diode that allows current to flow in only one direction, blocking the reverse half of each cycle

Explain what is meant by full wave rectification.

a process using a bridge of four diodes that converts both halves of each cycle of an alternating current into current flowing in one direction