definitions Flashcards
radian
angle subtended at the centre by an arc of length equal to the radius of the cirlce
angular displacement
the angle swept at the centre of the circle by an object moving in a cirlce
angular speed
the rate of change of angular displacement
centripetal force
resultant force on an object towards the centre of the circle when the object is rotating round that circle at a constant speedne
what is newtons 2nd law motions
the resultant force of a body is proportional to the rate of change of momentum
critical speed (motion in a cirlce)
the minimum speed at which the string remains taught
gravitational field
force per unit mass
Newton’s law of gravitation
Any two point masses attract each other with a force that is directly proportional to the product of their masses and inversely proportional to the square of their separation
Gravitational field strength, g,
the gravitational force exerted per unit mass on an object placed at that point
gravitational potential
the work done per unit mass in bringing a point mass from infinity
Gravitational potential energy
work done per unit mass in bring a point mass from infinity to a point
why is Gravitational Potential always negative
at infinity it is zero, and work is done on a mass to move it away from another mass
oscillation
a back and forth movement from an equilibrium position
frequency
the number oscillations per second
angular frequency
rate of change of angular displacement
Simple Harmonic Motion (SHM)
a type of oscillation in which the acceleration fo a body is directly proportional to its displacement but acts in the opposite direction
dampening
an oscillation in which resistive forces cause the energy of the system to be transferred to the surroundings as internal energy
Resonance
when the frequency of the driving frequency is equal to the natural frequency of the oscillating system. system absorbs the maximum energy and has maximum amplitude
Critical dampening
the minimum dampening that causes the oscillating system to return to its equilibrium position in the minimum time without oscillating
electric field
force per unit positive charge
electric field strength
force experienced per unit charge
direction of an electric field
the direction of an isolated free positive charge in the field
Coulombs law
The electrostatic force between two charges is directly proportional to the product of the charges and inversely proportional to the square of the separation
Electric potential
Work done per unit positive charge in bring a small test charge from infinity to a defined point
potential gradient
the rate of change of electric potential with respect to displacement in the direction of the field
Electric potential energy
the work done in bringing a charge from infinty to that point
magnetic field
region where a force acts on a magnetic material
magnetic flux density
force acting per unit current per unit length on a current carrying conductor
hall effect
the process through which a p.d is produced across a conductor when an external magnetic field is applied to the current through the conductor
velocity selector
a device consisting of perpendicular electric and magnetic fields where charged particles with a specific velocity can be filtered
magnetic flux
product of magnetic flux density and the cross sectional area perpendicular to the direction of flux density
Magnetic flux linkage
the product of the magnetic flux and the number of turns in a coil
electromagnetic induction
the process of inducing an E.M.F when magnetic field lines are cut
Faraday’s law of electromagnetic induction
The magnitude of the induced EMF is directly proportional to the rate of magnetic flux linkage
Len’z law
the direction of the induced emf is such as to oppose the change producing it
Photon
massless quantum of electromagnetic energy
electronvolt
energy gained by an electron travelling through a potential difference
work function
the minimum energy required for photoelectrons to be emitted from the surface of the metal
intensity (quantum physics)
The number of photons striking the metal surface per second
photocurrent
The number of photoelectrons emitted per second
de broglie wavelength
Wavelength associated with particles
ionisation
when an electron gains enough energy to be removed from the atom entirely
ultrasound
a high frequency sound above the range of human hearing
specific acoustic impedance
the product of the speed of the ultrasound in a medium and the density of the medium
intensity reflection coefficient
the ratio of the intensity of the reflected wave relative to the incident wave
Attenuation of ultrasound matter
the reduction of energy due to the absorption of ultrasound as it travels through a materialo
contrast
the difference in the degree of blackening between structure
sharpness
how well defined the edged of structures are
Positron emission tomography (PET)
a medical procedure that images tissues and organs by measuring the metabolic activity of the cells of the body
Annihiliation
when a particle meets its equivalent antiparticle they are both destroyed and their mass is converted into energy
Thermal equilibrium
when there is no net transfer of heat
heat
A form of energy that is transferred from a region of higher temperature to a region of lower temperature
Specific heat capacity
The amount of heat required to change a unit mass of the body by 1 degree Celsius
Specific latent heat
the amount of energy required to change the state of a unit mass without changing the temperature
avogrados law
equal volumes of all gases at the same temperature and pressure contain equal number of molecules
internal energy
the sum total of a random distribution of all molecules potential and kinetic energies
ideal gas
gas that obeys pv proportional to T, where T is thermodynamic temperature
first law of thermodynamics
U=q+w the increase in internal energy of a body is equal to the thermal energy transferred to it by heating plus the mechanical work done on it
root mean square value (rms)
the value of steady d.c that produces the same heating effect in the same resistor
rectification
the process of converting an alternating voltage into direct voltage
smoothing
the process of reducing the variation in the rectified voltage
decay constant
the probability that an individual nucleus will decay per unit of time
activity (Bq)
the rate of decay of nuclei of a radioactive source
half-life
the time taken for a radioactive nuclide to decay to half its original value
radioactive decay
the spontaneous disintegration of a nucleus to form a more stable nucleus, resulting in the emission of an alpha, beta or gamma particle
mass defect
the difference between the mass of a nucleus and the sum of the individuals masses of it protons and neutrons is
binding energy
the minimum amount of energy required to break a nucleus into its protons and neutron to infinity
binding energy of a nucleon
the binding energy of a nucleus divided by the number of nucleons in the nucleus
nuclear fusion
the fusing together of two small nuclei to produce a larger nucleus
nuclear fission
the splitting of large atomic nucleus into smaller nuclei
redshift
the fractional increase in wavelength due to the source and observer receding from each other
Hubble’s law
the recession speed of galaxies moving away from earth is proportional to their distance from the earth
wien’s displacement law
the black body radiation curve for different temperatures peaks at a wavelength which is inversely proportional to the temperature
A black body
an object in which absorbs all the radiation that falls on it, and is also a good emitte
stefan boltzman law
the total energy emitted by a black body per unit are per second is proportional to the fourth power of the absolute temperature of the body
luminosity
the total power output of radiation emitted by a star
Radiant flux intensity
the radiant power transmitted normally through a surface per unit area
standard candle
as astronomical object which has a known luminosity due to a characteristic quality possessed by that class of object
