Definitions Flashcards
Absolute Zero
The lowest possible temperature at which substances have the minimum internal energy
Acoustic Impedence
The product of the density of a substance and the speed of ultrasound in that substance
Aphelion
The furthest point from the sun in an orbit
Archimedes’ Principle
The upthrust of an object is equal to the weight of fluid displaced
Attenuation
The decrease in the intensity of electromagnetic radiation as it passes through matter or space
Brownian motion
The continuous random motion of small particles suspended in a fluid, visible under a microscope
Chandrasekhar limit
The mass of a stars core beneath which the electron degeneracy pressure is sufficient to prevent gravitational collapse.
1.44 Solar masses
Coherance
Two waves sources, or waves, that are coherent have a constant phase difference
Cosmological principle
The assumption that the universe, when viewed on a large scale, is homogeneous and isotropic and the laws of physics applies everywhere
Coupling gel
A gel with the acoustic impedance similar to that of skin, that is smeared onto the transducer and the patients skin before and ultrasound scan in order to fill air gaps and ensure that almost all the ultrasound enters the patients body
Decay constant
The probability of a decay of an individual nucleus per unit of time
Faradays law
The magnitude of the induced EMF is directly praportional to the rate of change of flux linkage
Fundamental frequency
The lowest possible frequency at which an object can vibrate
Ideal gas
A model of a gas including assumptions similar to the behaviour of a real gas
Inelastic collision
A collision in which kinetic energy is transferred into other forms and is NOT conserved
Interference pattern
A pattern of constructive and destructive interference formed as waves overlap
Keplar’s First law of planetary motion
The orbit of a planet is an ellipse with the sun as one of the foci
Keplar’s Second law of planetary motion
A line segment connecting the planet and the sun sweeps out equal areas during equal intervals of time
Keplar’s Third law of planetary motion
The square of the orbital period is directly proportional to the cube of is average distance from the sun
Kirchoff’s First law
At any point in an electrical circuit, the sum of currents into that point is equal to the sum of the currents out of that point.
Electrical charge is conserved
Kirchoff’s Second law
In a closed loop of an electrical circuit, the sum of the EMF’s is equal to the sum of the PD’s
Lenz’s law
The direction of the induced EMF or current is always such as to oppose the change producing it
Light Year
The distance travelled by light in a VACUUM in a time of one year
Lost volts
The potential difference across the internal resistor of a source of EMF
Internal resistance
The resistance of a source of EMF due to its construction which causes a loss in energy/voltage as the charge passes through the source
Magnetic field lines
Lines of force drawn to represent a magnetic field pattern
Magnetic flux
The product of the component of the magnetic flux density perpendicular to a given area and that cross-sectional area.
ø = BACosθ
Magnetic flux density
The strength of a magnetic field
Defined by the equation B = F/IL
Magnetic flux linkage
The product of the number of turns in a coil N and the magnetic flux
Maxwell - Boltzmann distribution
The distribution of the speeds of a particles in a gas
Newtons first law of motion
A body will remain at rest of continue moving at a constant velocity unless acted upon by a resultant force
Newtons Second Law of Motion
The rate of change of momentum is directly proportional to the resultant force and takes place in the direction of the force
Newtons Third Law
When two objects interact, each exerts and equal but opposite force and takes place in direction of the force
Newtons Laws of gravitation
The force between two point masses is directly proportional to the product of the masses and inversely proportional to the square of the separation between them
Ohm’s Law
The potential difference across a conductor is directly proportional to the current in the component as long as its temperature remains constant
Parallax angle
The angle of the apparent shift in the position of a relatively close star against the backdrop of much more distant stars as the earth makes half a rotation of the sun
Parsec
The distance at which the radius of one AU subtends an angle of one arcsecond
Perihelion
The closest point to the sun in an orbit
Phase difference
The difference between the displacements of particles along a wave
Or the difference between the displacements of particles on different waves
Measured in degrees or radians
Plane Polarised
Description of a transverse wave in which the oscillations are limited to only one plane
Resonance
The increase in amplitude of a forced oscillation when the driving frequency matches the natural frequency of oscillating system.
Semiconductor
A material with a lower number density than a typical conductor
Specific latent heat
The energy required to change the phase per unit of mass while at a constant temperature
Stellar parallax
A technique used to determine the distance of stars that are relatively close to the earth by comparing their apparent positions against distant stars at times 6 months apart
Threshold Voltage
The minimum potential difference at which a diode begins to conduct
Wave-particle duality
A theory that states that matter has both particle and wave properties and also electromagnetic radiation has wave and particulate nature
Wein’s Displacement Law
The peak wavelength (λmax) at which the radiation of a black body is a maximum, is inversely proportional to the absolute temperature of the black body.
Youngs Modulus
The ratio of the tensile stress to tensile strain when these quantities are directly proportional to each other
Binding energy
The minimum energy required to completely separate a nucleus into its constituent protons and neutrons
Black body
An idealised object that absorbs all the electromagnetic radiation incident on it and when in thermal equilibrium emits a characteristic distribution of wavelengths at a specific temperature
Gravitational Field
A field created around any object with mass, extending to infinity, but diminishing as distance from the centre of mass of the object increase
Gravitational field strength
The gravitational force exerted per unit of mass at a point within a gravitational field
Gravitational potential
The work done per unit of mass to bring an object from infinity to a point in the gravitational field
Gravitational potential energy
The capacity for doing work as a result of an objects position in a gravitational field
Hooked law
The force applied is directly proportional to the extension of the spring unless the limit of proportionality is exceeded
Hubbles constant
The gradient of a graph of a line of best fit for a plot of recessional speed against distance from the earth of other galaxies
Hubbles law
The recessional speed of a galaxy is almost directly proportional to its distance from Earth
