A2 Level Physics Definitions Flashcards
Angular speed
The angular displacement per unit
Centripetal force
The resultant force on an object towards the centre of the circle when the object is rotating round that circle at constant speed.
Centripetal acceleration
The acceleration of an object towards the centre of the circle when the object is rotating at constant speed round that circle.
Gravitational field
A region in space where a mass experiences a gravitational force.
Newton’s law of gravitation
Any two point masses attract each other with a force that is directly proportional to the produce of their masses and inversely proportional to the square of their separation.
Gravitational field strength
The gravitational field strength at a point is the gravitational force exerted per unit mass on a small object placed at that point.
Gravitational potential
The gravitational potential at a point is the work done per unit mass in bringing a point mass from infinity.
Geostationary orbit
An orbit of a satellite such that the satellite remains directly above the same point of the Earth at all times.
Natural frequency
The frequency at which a body vibrates when there is no (resultant external) resistive force acting on it.
Damped
A damped oscillation is an oscillation in which resistive forces cause the energy of the system to be transferred to the surroundings as internal energy.
Resonance
Occurs when the frequency of the driving force is equal to the natural frequency of the oscillating system. The system absorbs the maximum energy from the driver and has maximum amplitude.
Internal energy
The sum of the random distribution of kinetic and potential energies of the atoms or molecules in a system.
Isothermal change
A change of a system in which the temperature remains constant.
Specific latent heat of fusion
The amount of heat energy per unit mass needed to convert unit mass of solid to liquid without change in temperature.
Specific latent heat of vaporisation
The amount of heat energy per unit mass needed to convert unit mass of liquid to gas without a change in temperature.
Boyle’s law
The pressure exerted by a fixed mass of gas is inversely proportional to its volume, provided the temperature of the gas remains constant.
Charles’s law
The volume occupied by a gas at constant pressure is directly proportional to its thermodynamic (absolute) temperature.
Ideal gas
A gas that behaves according to the equation pV=Nrt.
Kinetic theory of gases
A model based on the microscopic motion of atoms or molecules of a gas.
Root-mean-square speed
The square root of the average of the squares of the speeds of all the molecules in a gas.
Electric field
A region where a charged object experiences a force.
Field of force
A region of space where an object feels a force; the force may be gravitational, electric, magnetic and so on.
Electric field strength (at a point)
The force per unit charge exerted on a stationary positive charge at that point.
Coulomb’s law
Any two point charges exert an electrical force on each other that is proportional to the product of their charges and inversely proportional to the square of the distance between them.
Electric potential
The electric potential at a point is equal to the work done per unit charge in bringing unit positive charge from infinity to that point.
Capacitance
The capacitance of a capacitor is the charge on the plates of the capacitor per unit potential difference across the plates.
Diffraction
The spreading of a wave when it passes through the gap or past the edge of an object
Photoelectric effect
An interaction between a photon and an electron in a metal, in which the electron is removed from the surface of a metal
Photon
A quantum of electromagnetic energy
Threshold frequency
The minimum frequency of the incident electromagnetic radiation that would eject electrons from the surface of a metal.
Threshold wavelength
The longest wavelength of the incident electromagnetic radiation that would eject electrons from the surface of a metal
Work function (energy)
The minimum energy needed by an electron to free itself from the surface of a metal.
Ground state
The lowest energy state that can be occupied by an electron in an atom.
de Broglie Wavelength
The wavelength associated with a moving particle, given by the equation: l=h/p
Mass defect
The difference between the total mass of the individual separate nucleons and the mass of the nucleus.
Binding energy
The minimum external energy required to completely separate all the neutrons and protons of a nucleus to infinity.
Fission
The process in which a massive nucleus splits into two smaller nuclei.
Fusion
The process in which two light nuclei join together to form a heavier nucleus.
Decay constant
The probability that an individual nucleus will decay per unit time interval.
Activity
The rate of decay of nuclei of a radioactive source. The units of activity is the becquerel, Bq.
Exponential decay
The decrease of a quantity where the rate of decrease is proportional to the value of quantity.
Half-life
The half-life t1/2 of an isotope is the mean time taken for half of the active nuclei in a sample to decay.
Intensity
Power per unit cross sectional area.
Attenuation
The gradual decrease of intensity of radiation as it passes through a medium.
Attenuation (absorption) coefficient
The attenuation (or absorption) coefficient of a material is a constant that depends on the material and the frequency of the X-rays
Contrast
The difference in brightness between the brightest and the dark areas
Image intensifiers
A device used to change a low-intensity X-ray image into a bright visual image
Contrast media
Materials, such as barium, which are good absorbers of X-rays; they are used to show the edges of soft tissues in X-ray images
Computerised axial tomography (CAT or CT)
A technique in which X-rays are used to image the body in order to produce a three-dimensional image
Piezo-electric crystal
A material that produces an e.m.f. when it is stressed, causing its shape to change. Also, when a voltage is applied across it in one direction, it changes its dimensions slightly.
Acoustic impedance
The product of the density of the substance and the speed of the ultrasound in the substance.
Piezo-electric effect
The production of an e.m.f. across a crystal by putting the crystal under stress. The opposite effect is applying a p.d. across the crystal causing it to change shape.
Impedance matching
The use of a gel to reduce the intensity of unwanted, reflected ultrasound between two materials. The gel has a similar acoustic impedance to the reflecting material.
Radiotracer
A substance that consists of radioactive material that is attached to a natural chemical, such as glucose.
Line of response
A line drawn from the PET detector triggered by one g-ray to the opposite detector that was triggered by the second g-ray.
