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OCR Physics A2 > DEFINITIONS > Flashcards

DEFINITIONS Flashcards

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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

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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.

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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

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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.

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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

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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.

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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

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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

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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.

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10
Q

Absolute/thermodynamic scale of temperature

A

is independent of the properties of any specific substance. Measured in kelvin, K.

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11
Q

Absolute zero

A

(0K) is the temperature at which a substance has minimum internal energy; this is the lowest limit for temperature.

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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.

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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.

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14
Q

Internal energy

A

the sum of the randomly distributed kinetic and potential energies of all atoms or molecules within a system

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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.

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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

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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.

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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.

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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.

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20
Q

Ideal gas

A

A gas that has internal energy only in the form of random kinetic energy.

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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.

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22
Q

Root mean square (r.m.s.) speed

A

Is the square root of the mean square speed.

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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

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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

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25
Q

Boltzmann constant, k

A

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.

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26
Q

1 radian

A

The angle subtended at the centre of a circle when the arc is equal in length to the radius of the circle.

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27
Q

Time period

A

The time taken in seconds for one complete circular path.

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28
Q

Angular velocity

A

the rate of angular rotation, measured in radians per second rad s^-1.

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29
Q

Centripetal acceleration

A

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.

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30
Q

Centripetal force

A

The resultant force on an object, acting towards the centre of the circle, causing it to move in a circular path.

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31
Q

Displacement

A

The distance an object moves from its equilibrium position, may be positive or negative.

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32
Q

Amplitude

A

Xo, the max displacement and will always be positive.

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33
Q

Frequency

A

The number of oscillations per unit time at any point.

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34
Q

Period (oscillations)

A

The time taken for one complete pattern of oscillation at any point.

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35
Q

Angular frequency

A

the product 2pief or alternatively w = 2pie/T, has units of radians per second.

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36
Q

Phase difference

A

phi, Is the fraction of a complete cycle or oscillation between 2 oscillating points, expressed in degrees or radians.

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37
Q

Simple harmonic motion

A

When the acceleration of a body is directly proportional to its displacement from a fixed point and always directed towards that fixed point.

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38
Q

Isochronous

A

The period of an object is constant and independent of the amplitude of the oscillation.

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39
Q

Damping

A

Forces which reduce the amplitude of an oscillation with time, due to energy being removed from the oscillating system.

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40
Q

Free oscillations

A

Occur when there is no external, periodic. The system oscillates at its natural frequency.

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41
Q

Natural frequency

A

The frequency at which a system will oscillate when undergoing free oscillations.

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42
Q

Forced oscillations

A

Occur when an external force or driving force is applied to keep the body oscillating. The system oscillates

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43
Q

Driving frequency

A

The frequency of the driving force applied to an oscillating object.

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44
Q

Resonance

A

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.

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45
Q

Nuclear fusion

A

The process of 2 nuclei Koenig together and releasing energy from a change in binding energy.

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46
Q

Gravitational collapse

A

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.

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47
Q

Radiation pressure

A

Created by the momentum of photons released in fusion reactions, and acts outwards.

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48
Q

Gas pressure

A

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.

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49
Q

Main sequence star

A

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.

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50
Q

Red giant

A

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.

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51
Q

White dwarf

A

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.

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52
Q

Planetary nebula

A

An expanding, glowing shell of ionised hydrogen and helium ejected from a red giant star at the end of its life.

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53
Q

Electron degeneracy pressure

A

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.

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54
Q

Red super giant

A

A star that has exhausted all the hydrogen in its core and has a mass much higher than the sun.

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55
Q

Chandrasekhar limit

A

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.

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56
Q

Supernova

A

a huge explosion produced when the core of a red giant collapses,

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57
Q

Neutron star

A

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.

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58
Q

Black hole

A

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).

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59
Q

Hertzsprung-Russell diagram

A

Luminosity against temperature graph

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60
Q

Luminosity of a star

A

The total energy that a star emits per second.

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61
Q

Continuous spectrum

A

A spectrum that appears to contain all wavelengths over a comparatively wide range.

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62
Q

Energy levels

A

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.

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63
Q

Emission line spectrum

A

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
Q

Absorption line spectrum

A

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
Q

Transmission diffraction grating

A

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
Q

Maxima

A

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
Q

Wiens displacement law

A

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
Q

Stefans law

A

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
Q

Astronomical unit AU

A

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
Q

Parsec

A

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
Q

Stellar parallax

A

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
Q

Light year

A

The distance traveled by light in 1 year.

73
Q

Doppler effect/Doppler shift

A

The change in wavelength caused by the relative motion between the wave source and an observer.

74
Q

Red shift

A

The apparent increase in wavelength of electromagnetic radiation caused when the source e.g. a star is moving away, relative to the observer.

75
Q

Hubbles law

A

The recessional velocity of a galaxy is directly proportional to its distance, d from the earth.

76
Q

Hubble constant

A

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
Q

Cosmic microwave background radiation

A

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
Q

Big Bang theory

A

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
Q

The cosmological principle

A

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
Q

Dark matter

A

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
Q

Dark energy

A

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
Q

Capacitor

A

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
Q

Capacitance

A

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
Q

1 Farad

A

The unit of capacitance is the Farad. 1 farad is equivalent to one coulomb per volt.

85
Q

Exponential decay

A

Where the quantity decreases at a rate that is proportional to the magnitude of the quantity at that time.

86
Q

Time constant (capacitors)

A

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
Q

Electric field

A

The region around a body in which other charged bodies will feel a force due to the electric charge of the body.

88
Q

Electric field lines

A

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
Q

Electric field strength

A

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
Q

Coulombs law

A

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
Q

Permittivity of free space

A

e0 is a physical constant related to the size of the force between electric charges in free space (a vacuum).

92
Q

Permittivity

A

e, Is a constant related to the size of the capacitance of a capacitor.

93
Q

Relative permittivity

A

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
Q

Electric potential

A

Work done per unit positive charge to move that charge from infinity to a point in an electric field, units JC^-1.

95
Q

Electric potential energy

A

of a body of charge 1, is the work done to move that charge from infinity to a point in an electric field.

96
Q

Magnetic field

A

The region around a permanent magnet or a moving charge in which another body with magnetic properties will feel a force.

97
Q

Magnetic field lines

A

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
Q

Solenoid

A

A long coil of current carrying wire.

99
Q

Magnetic flux

A

The product of the magnetic flux density and the area at right angles to the flux. Measured in webers Wb.

100
Q

Magnetic flux density

A

A measure of the strength of a magnetic field in units Tesla T or Wb m^-2.

101
Q

1 weber

A

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
Q

Flemings left hand rule

A

Shows the direction of the force on a conductor carrying a current in a magnetic field.
Force - thumb
Field - first
Current - second

103
Q

Velocity selector

A

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
Q

Electromagnetic induction

A

The process of inducing an emf in a conductor when there is a change in magnetic flux linkage across the conductor.

105
Q

Induced emf

A

The emf produced by electromagnetic induction.

106
Q

Magnetic flux linkage

A

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
Q

Faraday’s law

A

..of electromagnetic induction states that the magnitude of the induced emf is equal to the rate of change of flux linkage.

108
Q

Lenz’s law

A

States that the direction of any induced emf or induced current is in a direction that opposes the flux change that causes it.

109
Q

Search coil

A

A small, flat coil used to determine the strength of a magnetic field.

110
Q

Generator

A

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
Q

Alternating current a.c.

A

Electrical current that reverses its direction with a constant frequency.

112
Q

Transformer

A

A device that can either increase or decrease the size of an alternating voltage with little loss of power.

113
Q

Efficiency (energy)

A

The ratio of useful output energy to total input energy.

114
Q

Unified atomic mass unit

A

defined as 1/12 of the mass of a carbon-12 atom.

115
Q

Proton number

A

The number of protons inside the nucleus of a particular atom. Also known as the atomic number,

116
Q

Nucleon number

A

The number of nucleons inside the nucleus of a particular atom. Also known as the mass number.

117
Q

Isotopes

A

Atoms of the same element which contain the same number of protons but can have varying numbers of neutrons.

118
Q

Strong nuclear force

A

Acts between nucleons and holds the nucleus together against the electrostatic repulsion of the protons.

119
Q

Fundamental particles

A

Particles that cannot be broken down into smaller components,

120
Q

Hadrons

A

Particles consisting of a combination of quarks to give a net zero or whole number charge. Neutrons and protons are hadrons,

121
Q

Leptons

A

Fundamental particles such as electrons and neutrinos.

122
Q

Quarks

A

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
Q

Neutrino

A

A fundamental particle (lepton) with almost no mass and zero charge. Each neutrino has an antimatter partner called an antineutrino.

124
Q

Weak nuclear force

A

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
Q

Antiparticle

A

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
Q

Alpha particle

A

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
Q

Beta particle

A

A high speed electron emitted from the nucleus during beta decay. It is produced when a neutron changes into a proton.

128
Q

Gamma ray

A

A form of EM wave with wavelengths between 10^-16 and 10^-9m. Emitted from the nucleus during gamma decay.

129
Q

Beta minus decay

A

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
Q

Beta plus decay

A

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
Q

Activity (nuclear decay)

A

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
Q

Decay constant

A

lambda, is the probability that an individual nucleus will decay per unit time. Units are s^-1, min^-1 or h^-1.

133
Q

Half life

A

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
Q

Carbon dating

A

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
Q

Annihilation

A

The process in which a particle and its antiparticle interact and their combined mass is converted to energy via E = mc^2.

136
Q

Pair production

A

The process of creating a particle-antiparticle pair from a high energy photon.

137
Q

Mass defect

A

The difference ein mass between the mass of a nucleus and the total mass of its separate nucleons.

138
Q

Binding energy

A

…of a nucleus, is the minimum energy required to separate the nucleus into its constituent parts.

139
Q

Induced nuclear fission

A

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
Q

Chain reaction

A

The sequence of nuclear reactions produced when an induced nuclear fission reaction triggers more than one further fission reaction.

141
Q

Control rod

A

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
Q

Moderator

A

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
Q

Compton scattering

A

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
Q

Attenuation

A

A gradual decrease in intensity.

145
Q

Attenuation (or absorption) coefficient

A

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
Q

Computerised axial tomography (CAT)

A

Process using multiple x ray scans to produce images of slices through the body in one plane, in order to produce a 3D.

147
Q

Tracer

A

A radioattive substance either ingested by, or injected into a patient. It emits gamma photons to be detected by a gamma camera.

148
Q

Gamma camera

A

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
Q

Collimator

A

A device for producing parallel-sided (collimated) beam of em radiation.

150
Q

Scintillator

A

A material that produces many photons of visible light when struck by a high energy photon,

151
Q

Photomultiplier tube

A

A device used to give a pulse of electrons for each incident photon.

152
Q

Positron elision tomography (PET)

A

The use of gamma photons produced when positrons annihilate with electrons inside the body to map out biologically active areas within the body.

153
Q

Ultrasound

A

Longitudinal waves above the upper limit of the audible range, with frequencies greater than 20,000Hz.

154
Q

Transducer

A

A device such as a microphone, which converts a non electric signal e.g. sound into an electrical signal

155
Q

Piezoelectric effect

A

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
Q

Acoustic impedance

A

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
Q

Impedance matching

A

The reduction in intensity of reflected ultrasound at the boundary between 2 substances, achieved when the 2 substance have similar or identical acoustic impedances.

OCR Physics A2 (15 decks)

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