DEFINITIONS Flashcards
1
Q
Gravitational field definition
A
Region around a body in which other bodies will feel a force due to the mass of the body
2
Q
Gravitational field lines definition
A
Show the shape of the field and the direction of the field line at a point is the direction in which a small mass would move when placed at that point.
3
Q
Gravitational field strength definition
A
At any point in a gravitational fields is the force acting per unit mass at that point. Units are Nkg-1
4
Q
Newtons law of gravitation
A
States that the gravitational force of attraction between two point masses is directly proportional to the product of their masses and inversely proportional to the square of their separation.
5
Q
Kepler third law
A
States that the square of the period of a planet orbiting the sun is proportional to the mean radius of its orbit cubed. Kepler law also applies to other planetary systems such as orbits of moons and binary stars
6
Q
Geostationary orbit
A
An orbit of the earth made by a satellite that has the same time period and orbital direction as the rotation of the earth and is in the equatorial plane.
7
Q
Gravitational potential
A
At a point in a gravitational field is defined as the work done in moving unit mass from infinity (GPE is 0) to that point. Unit Jkg-1
8
Q
Gravitational potential energy
A
Of a mass m in a gravitational field depends on its position in the field. For a radial field around a point or spherical mass M, the gpe at a distance r, from M is defined as -(GMm)/r
9
Q
Escape velocity
A
From a point in a gravitational field is the minimum launch velocity required to move an object from that point to infinity.
10
Q
Absolute/thermodynamic scale of temperature
A
is independent of the properties of any specific substance. Measured in kelvin, K.
11
Q
Absolute zero
A
(0K) is the temperature at which a substance has minimum internal energy; this is the lowest limit for temperature.
12
Q
Thermal equilibrium
A
Objects in contact with each other and at the same temperature; meaning there is no net heat flow between them.
13
Q
Kinetic model of matter
A
Where all matter is made up of very small particles (atoms, molecules or ions) which are in constant motion. The model allows us to explain the properties of matter and changes of phase in terms of the arrangement of the particles, the motion of the particles and the attractive forces between them.
14
Q
Internal energy
A
the sum of the randomly distributed kinetic and potential energies of all atoms or molecules within a system
15
Q
Brownian motion
A
The random movement of small visible particles suspended in a fluid (e.g. smoke particles in air) due to collisions with much smaller, randomly moving atoms or molecules of the fluid.
16
Q
Specific heat capacity
A
the amount of energy needed to raise the temperature of 1kg of the substance by 1K. The units are Jkg^-1K^-1
17
Q
Specific latent heat of fusion
A
Lf, the amount of energy required to change the phase of 1kg of a substance from a solid to a liquid.
18
Q
Specific latent heat of vaporisation
A
Lv, the amount of energy required to change the phase of 1kg go a substance from a liquid to a gas.
19
Q
1 mole
A
The amount of a substance that contains as many particles as 12grams of carbon-12. One mole of a substance will contain 6.02 x 10^23 particles. This number is known as avogadros constant and has symbol NA.
20
Q
Ideal gas
A
A gas that has internal energy only in the form of random kinetic energy.
21
Q
Mean square speed
A
The mean value of the square of velocity c for a large number of gas particles (atoms or molecules) moving randomly in a gas. The bar indicates an average.
22
Q
Root mean square (r.m.s.) speed
A
Is the square root of the mean square speed.
23
Q
Boyle’s law
A
The volume of a fixed mass of gas is inversely proportional to the pressure exerted on the gas, under conditions of constant temperature.
pV = constant under conditions of constant temperature.
p1V1 = P2V2
24
Q
Equation of state of an ideal gas (ideal gas equation)
A
Links the pressure of a gas (p) with the volume (V), molar gas constant (R), number of moles of gas (n) and temperature (T).
pV = nRT
25
Boltzmann constant, k
A constant used when relating the temperature of the gas to the mean translational kinetic energy of the particles in the gas. It can also be thought of as the gas constant for a single molecule.
26
1 radian
The angle subtended at the centre of a circle when the arc is equal in length to the radius of the circle.
27
Time period
The time taken in seconds for one complete circular path.
28
Angular velocity
the rate of angular rotation, measured in radians per second rad s^-1.
29
Centripetal acceleration
The acceleration of an object moving with uniform circular motion. The centripetal acceleration is directed radially inwards towards the centre of the circle, perpendicular to the velocity vector at any instant.
30
Centripetal force
The resultant force on an object, acting towards the centre of the circle, causing it to move in a circular path.
31
Displacement
The distance an object moves from its equilibrium position, may be positive or negative.
32
Amplitude
Xo, the max displacement and will always be positive.
33
Frequency
The number of oscillations per unit time at any point.
34
Period (oscillations)
The time taken for one complete pattern of oscillation at any point.
35
Angular frequency
the product 2pief or alternatively w = 2pie/T, has units of radians per second.
36
Phase difference
phi, Is the fraction of a complete cycle or oscillation between 2 oscillating points, expressed in degrees or radians.
37
Simple harmonic motion
When the acceleration of a body is directly proportional to its displacement from a fixed point and always directed towards that fixed point.
38
Isochronous
The period of an object is constant and independent of the amplitude of the oscillation.
39
Damping
Forces which reduce the amplitude of an oscillation with time, due to energy being removed from the oscillating system.
40
Free oscillations
Occur when there is no external, periodic. The system oscillates at its natural frequency.
41
Natural frequency
The frequency at which a system will oscillate when undergoing free oscillations.
42
Forced oscillations
Occur when an external force or driving force is applied to keep the body oscillating. The system oscillates
43
Driving frequency
The frequency of the driving force applied to an oscillating object.
44
Resonance
Occurs when the driving frequency is equal to the natural frequency of the system being forced to oscillate. This result sin the body oscillating at its natural frequency and maximum amplitude.
45
Nuclear fusion
The process of 2 nuclei Koenig together and releasing energy from a change in binding energy.
46
Gravitational collapse
The inward movement of material in a star due to the gravitational force caused by its own mass. Star formation is due to the gradual gravitational collapse of a cloud of gas and dust. Gravitational collapse occurs in a mature star when the internal gas and radiation pressure can no longer support the stars mass.
47
Radiation pressure
Created by the momentum of photons released in fusion reactions, and acts outwards.
48
Gas pressure
p, is related to the temperature, T, and volume, V, of a gas using pV = nRT, and also to the mean square speed of the gas atoms using pV = 1/3 Nm*(rmsc). Gas pressure acts in all direction at a point inside a gas such as inside a star.
49
Main sequence star
A star in the main part of its life cycle, where it is fusing hydrogen to form helium in its core. The main sequence stars are shown as a curved band on a plot of a stars luminosity against temperature.
50
Red giant
A star in its later stages of its life that has nearly exhausted the hydrogen in its core and is now fusing helium nuclei. It is bigger than a normal star because its surface layers have cooled and expanded.
51
White dwarf
The end product of a low mass star, when the outer layers have dispersed into space. A white dwarf is very dense, with a high surface temperature and low luminosity.
52
Planetary nebula
An expanding, glowing shell of ionised hydrogen and helium ejected from a red giant star at the end of its life.
53
Electron degeneracy pressure
The pressure that stops the gravitational collapse of a low mass star (below Chandrasekhar limit). This is the pressure that prevents a white dwarf from collapsing.
54
Red super giant
A star that has exhausted all the hydrogen in its core and has a mass much higher than the sun.
55
Chandrasekhar limit
the max possible mass for a stable white dwarf star and is equal to 1.4 times the mass of out sun. White dwarfs with masses above this will collapse further to become neutron stars or black holes.
56
Supernova
a huge explosion produced when the core of a red giant collapses,
57
Neutron star
The remains of the core of a red super giant after it has undergone a supernova explosion. It is incredibly dens and composed mainly of neutrons.
58
Black hole
The core of a massive star that has collapsed almost to a point. Black holes are very dense and small, with a gravitational field so strong that light cannot escape (the escape velocity is greater the speed of light).
59
Hertzsprung-Russell diagram
Luminosity against temperature graph
60
Luminosity of a star
The total energy that a star emits per second.
61
Continuous spectrum
A spectrum that appears to contain all wavelengths over a comparatively wide range.
62
Energy levels
The specific energies that electrons can have when occupying specific orbits. Electrons can only occupy these discrete energy levels and cannot exist at other energy values between them.
63
Emission line spectrum
The spectrum of frequencies of electromagnetic radiation emitted due to electron transitions from a higher energy level to a lower one within an atom of that element. Since there are many possible electron transitions for each atom, there are many different radiated wavelengths. A line spectrum consist of a series of bright lines against a dark background.
64
Absorption line spectrum
The pattern of dark line sin a continuous spectrum from a light source and is caused by light passing through an absorbing medium such as a gas. The dark lines represent the wavelengths that are absorbed.
65
Transmission diffraction grating
A glass surface with a large number of very fine parallel grooves or slits, and used to produce optical spectra by diffraction of transmitted light.
66
Maxima
Regions of brightness which will be seen when the path difference between overlapping waves is equal to a whole number of wavelengths.
nlambda = dsintheta, where n = 0, 1, 2, 3...
67
Wiens displacement law
states that lambda max is proportional to 1/T or lambda max*T = constant, where T is temperature on the absolute Kelvin scale. It is used to estimate ether peak surface temperature of a star from the wavelength at which the stars brightness is maximum.
68
Stefans law
Relates the luminosity L of a star with its absolute temperature T: L = 4pier^2sigmaT^4, where the constant sigma is Stefan's constant.
69
Astronomical unit AU
The mean distance form the centre of the earth to the centre of the sun = 1.5 x 10^8 km or 1.5 x 10^11 m
70
Parsec
Unit of distance that gives a parallax angle of 1 second of arc (1/3600 of a degree), using the radius of the earths orbit (1AU) as the baseline of a right angled triangle.
71
Stellar parallax
The apparent shifting in position of a star viewed against. background of distant stars when viewed from different positions of the earth, such as at different position of the earths orbit around the sun.
72
Light year
The distance traveled by light in 1 year.
73
Doppler effect/Doppler shift
The change in wavelength caused by the relative motion between the wave source and an observer.
74
Red shift
The apparent increase in wavelength of electromagnetic radiation caused when the source e.g. a star is moving away, relative to the observer.
75
Hubbles law
The recessional velocity of a galaxy is directly proportional to its distance, d from the earth.
76
Hubble constant
Ho, is the constant of proportionality in the equation v = Hod. The SI unit for Ho is s^-1 but it can also be quoted in Kms^-1Mpc^-1.
77
Cosmic microwave background radiation
Microwave radiation received from all over the sky originating from after the Big Bang, when the universe had cooled to a temperature near 3000K. As the universe expanded this radiation is now just a faint microwave glow with a peak wavelength corresponding to a temp of 2.7K.
78
Big Bang theory
States that the universe was created from a single point where all of the universe's current mass was situated. At the time of its creating, the universe was much smaller, hotter and denser than it is now. Time and space were both created at the instant of the Big Bang.
79
The cosmological principle
States that on a large scale the universe is isotropic (same in all directions), and homogenous (uniform density as long as large enough volume is considered).
80
Dark matter
Matter which cannot be seen and that does not emit or absorb electromagnetic radiation. It is not detected directly, but is detected indirectly based on its gravitational effects relating to either the rotation of galaxies or by gravitational lensing of starlight.
81
Dark energy
A type of energy that permeates the whole universe and opposes the attractive force of gravitation between galaxies via the exertion of a negative pressure. It is not detected directly but we know it exists because we now know the universe is accelerating as it expands.
82
Capacitor
A circuit component that stores energy by separating charges onto 2 electrical conductors (plates) with an insulator between them. One plate becomes positively charged and the other becomes negatively charged.
83
Capacitance
The capacitance of a capacitor is defined as the quantity of charge which can be stored per unit pd, across the plates of the capacitor.
84
1 Farad
The unit of capacitance is the Farad. 1 farad is equivalent to one coulomb per volt.
85
Exponential decay
Where the quantity decreases at a rate that is proportional to the magnitude of the quantity at that time.
86
Time constant (capacitors)
the time taken for the charge remaining on a capacitor to decrease to 1/e (about 37%) of its initial value, measured in seconds. Can be found from t = CR.
87
Electric field
The region around a body in which other charged bodies will feel a force due to the electric charge of the body.
88
Electric field lines
Show the shape of the field and the direction of the field line at a point is the direction in which a small positive charge would move when placed at that point.
89
Electric field strength
The force per unit positive charge. Units are NC^-1. The force that a charge of +1 C would experience if placed at that point in the field.
90
Coulombs law
States that the electrical force between 2 point charges is directly proportional to the product of their charges and inversely proportional to the square of their separation.
91
Permittivity of free space
e0 is a physical constant related to the size of the force between electric charges in free space (a vacuum).
92
Permittivity
e, Is a constant related to the size of the capacitance of a capacitor.
93
Relative permittivity
er, of a material is the factor by which the capacitance of a capacitor with that material between its plates is increased relative to the capacitance of a capacitor with air or vacuum between its plates. It is a pure number and has no units.
94
Electric potential
Work done per unit positive charge to move that charge from infinity to a point in an electric field, units JC^-1.
95
Electric potential energy
of a body of charge 1, is the work done to move that charge from infinity to a point in an electric field.
96
Magnetic field
The region around a permanent magnet or a moving charge in which another body with magnetic properties will feel a force.
97
Magnetic field lines
Show the shape of the field and the direction. The direction of the field line at a point shows the direction which a plotting compass would point.
98
Solenoid
A long coil of current carrying wire.
99
Magnetic flux
The product of the magnetic flux density and the area at right angles to the flux. Measured in webers Wb.
100
Magnetic flux density
A measure of the strength of a magnetic field in units Tesla T or Wb m^-2.
101
1 weber
The magnetic flux when a magnetic field of magnetic flux density 1 Tesla passes at right angles through an area of one square metre.
102
Flemings left hand rule
Shows the direction of the force on a conductor carrying a current in a magnetic field.
Force - thumb
Field - first
Current - second
103
Velocity selector
A device using perpendicular magnetic and electric fields to select charged particles travelling at a specific velocity, which leave the region of crossed fields undeflected.
104
Electromagnetic induction
The process of inducing an emf in a conductor when there is a change in magnetic flux linkage across the conductor.
105
Induced emf
The emf produced by electromagnetic induction.
106
Magnetic flux linkage
For a coil equals the product of the magnetic flux through the coil and the number of turns on the coil. units Weber turns.
107
Faraday's law
..of electromagnetic induction states that the magnitude of the induced emf is equal to the rate of change of flux linkage.
108
Lenz's law
States that the direction of any induced emf or induced current is in a direction that opposes the flux change that causes it.
109
Search coil
A small, flat coil used to determine the strength of a magnetic field.
110
Generator
A device used to generate electricity, in which the work done to turn the coil within the magnetic field is transferred to electrical energy. The rotation of a coil within a magnetic field produces a constantly changing flux linkage through the coil. This in turn produces a constantly changing induced emf in the coil.
111
Alternating current a.c.
Electrical current that reverses its direction with a constant frequency.
112
Transformer
A device that can either increase or decrease the size of an alternating voltage with little loss of power.
113
Efficiency (energy)
The ratio of useful output energy to total input energy.
114
Unified atomic mass unit
defined as 1/12 of the mass of a carbon-12 atom.
115
Proton number
The number of protons inside the nucleus of a particular atom. Also known as the atomic number,
116
Nucleon number
The number of nucleons inside the nucleus of a particular atom. Also known as the mass number.
117
Isotopes
Atoms of the same element which contain the same number of protons but can have varying numbers of neutrons.
118
Strong nuclear force
Acts between nucleons and holds the nucleus together against the electrostatic repulsion of the protons.
119
Fundamental particles
Particles that cannot be broken down into smaller components,
120
Hadrons
Particles consisting of a combination of quarks to give a net zero or whole number charge. Neutrons and protons are hadrons,
121
Leptons
Fundamental particles such as electrons and neutrinos.
122
Quarks
Components of hadrons, and have a fractional electric charge. To date, they are believed to be fundamental particles. There are different types of quark including up, down and strange quarks.
123
Neutrino
A fundamental particle (lepton) with almost no mass and zero charge. Each neutrino has an antimatter partner called an antineutrino.
124
Weak nuclear force
Felt by both quarks and leptons, it can change quarks from one type to another or leptons from one type to another and is responsible for beta decay.
125
Antiparticle
A particle of antimatter that has the same rest mass but, if charged, the equal and opposite charge to its corresponding particle e.g. positron and electron.
126
Alpha particle
A particle comprising 2 protons and 2 neutrons ejected from the nucleus during radioactive decay. It is identical to a helium nucleus and is emitted due to its unusually high stability as a particle.
127
Beta particle
A high speed electron emitted from the nucleus during beta decay. It is produced when a neutron changes into a proton.
128
Gamma ray
A form of EM wave with wavelengths between 10^-16 and 10^-9m. Emitted from the nucleus during gamma decay.
129
Beta minus decay
A neutron in the nucleus breaks down into a proton under the influence of the weak nuclear force, and a beta minus particle and an electron antineutrino are emitted. A beta minus particle is an electrons.
130
Beta plus decay
A protons in the nucleus breaks down into a neutron under the influence of the weak nuclear force, and a beta plus particle and an electron neutrino are emitted. A beta plus particle is a positron.
131
Activity (nuclear decay)
The number of nuclear (number of gamma rays emitted) decays per unit time. An activity of one decay per second is called one Bq.
132
Decay constant
lambda, is the probability that an individual nucleus will decay per unit time. Units are s^-1, min^-1 or h^-1.
133
Half life
t1/2, is defined as the mean time taken for the activity of a source, or the number of undecided nuclei present, to halve.
134
Carbon dating
A technique used to determine the age of organic matter from the relative proportions of the carbon-12 and carbon-14 isotopes that it contains, using the half life of carbon-14.
135
Annihilation
The process in which a particle and its antiparticle interact and their combined mass is converted to energy via E = mc^2.
136
Pair production
The process of creating a particle-antiparticle pair from a high energy photon.
137
Mass defect
The difference ein mass between the mass of a nucleus and the total mass of its separate nucleons.
138
Binding energy
...of a nucleus, is the minimum energy required to separate the nucleus into its constituent parts.
139
Induced nuclear fission
Occurs when a nucleus absorbs slow moving neutrons and the resulting unstable nucleus undergoes a fission reaction to split into 2 smaller nuclei and a small number of neutrons, releasing energy.
140
Chain reaction
The sequence of nuclear reactions produced when an induced nuclear fission reaction triggers more than one further fission reaction.
141
Control rod
A rod that can be lowered into the core of a nuclear reactor, absorb neutrons and slow down the chain reaction. Control rods are usually made from boron.
142
Moderator
A substance used in a nuclear reactor which slows down neutrons so that they have a greater chance of being absorbed by the fissile nuclear fuel. The moderator is usually made of graphite.
143
Compton scattering
The effect whereby an x ray deflected by interaction with an orbital electron has a longer wavelength than its initial wavelength. The electron is ejected from the atom at high speed.
144
Attenuation
A gradual decrease in intensity.
145
Attenuation (or absorption) coefficient
A constant used to calculate how the intensity of x rays decreases as they pass through a material. The unit is m^-1 or cm^-1
146
Computerised axial tomography (CAT)
Process using multiple x ray scans to produce images of slices through the body in one plane, in order to produce a 3D.
147
Tracer
A radioattive substance either ingested by, or injected into a patient. It emits gamma photons to be detected by a gamma camera.
148
Gamma camera
Detects gamma photons emitted from a patient given a radioactive tracer. This is used to produce a real time image of the path of the tracer through the body.
149
Collimator
A device for producing parallel-sided (collimated) beam of em radiation.
150
Scintillator
A material that produces many photons of visible light when struck by a high energy photon,
151
Photomultiplier tube
A device used to give a pulse of electrons for each incident photon.
152
Positron elision tomography (PET)
The use of gamma photons produced when positrons annihilate with electrons inside the body to map out biologically active areas within the body.
153
Ultrasound
Longitudinal waves above the upper limit of the audible range, with frequencies greater than 20,000Hz.
154
Transducer
A device such as a microphone, which converts a non electric signal e.g. sound into an electrical signal
155
Piezoelectric effect
The change in volume of a material when a pd is applied across its opposite faces. Alternatively, it is the production of an induced emf when certain crystals are placed under stress.
156
Acoustic impedance
Z, is defined by the equation Z = pC where p is density of the material and c is the speed of sound in the material. The unit is kg m^-2 s^-1.
157
Impedance matching
The reduction in intensity of reflected ultrasound at the boundary between 2 substances, achieved when the 2 substance have similar or identical acoustic impedances.
