Definitions Flashcards
All the key word definitions across all units.
1
Q
What is the absolute scale of temperature?
A
A scale for measuring temperature based on absolute 0 and the triple point of pure water, with graduations of equal size to those of the Celsius scale.
2
Q
What is absolute 0?
A
The lowest possible temperature, the temperature at which substances have minimum internal energy.
3
Q
What is an absorption coefficient?
A
A measure of absorption of x ray photons by a substance (also known as an attenuation coefficient).
4
Q
What is an absorption line spectrum?
A
A set of specific frequencies of electromagnetic radiation, visible as dark lines in an otherwise continuous spectrum on spectroscopy. They are absorbed by atoms as their electrons are excited between energy states by absorbing their corresponding amount of energy in the form of photons.
5
Q
Define “acceleration”
A
The rate of change of velocity.
6
Q
What is acceleration due to free fall?
A
The rate of change of an object falling in a gravitational field.
7
Q
What is acoustic impedance?
A
The product of density of a substance and the speed of ultrasound in that substance.
8
Q
What is acoustic matching?
A
The use of two substances with similar acoustic impedance to minimise reflection of ultrasound at the boundary between them.
9
Q
Define “Activity” in terms of Nuclear physics.
A
The rate of which nuclei decay or disintegrate in a radioactive source, measured in becquerels or counts per second.
10
Q
What is alpha radiation?
A
Ionising radiation consisting of particles comprising two protons and two neutrons with a charge of +2e.
11
Q
What is air resistance?
A
The resistive force experienced by objects travelling through air.
12
Q
What is an ammeter?
A
A device used to measure electric current, which must be placed in series and have 0 resistance.
13
Q
Define “amount of substance”.
A
A measure of the amount of a matter in moles.
14
Q
What is an Ampere?
A
The base SI unit for electric current. This is defined as the the current flowing in two parallel wires in a vacuum 1m apart such there is an attractive force of 2x10^-7 N per meter length of wire.
15
Q
Define “Amplitude”.
A
The maximum displacement from the equilibrium position.
16
Q
What is the angle of incidence?
A
The angle between the direction of travel of an incident wave and the normal boundary between the two media.
17
Q
What is the angle of reflection?
A
The angle between the direction of travel of the reflected wave and the normal boundary between the two media.
18
Q
Define “Angular Frequency”.
A
A quantity used in oscillatory motion - equal to the product of frequency and 2 Pi.
19
Q
What is angular velocity?
A
The rate of change for an object moving in a circular path.
20
Q
What is an anion?
A
A negatively charged ion, one which is attracted to an anode.
21
Q
Define “annihilation”.
A
The complete destruction of a particle and its antiparticle in an interaction that releases energy in the form of two identical photons.
22
Q
What is an anode?
A
A positively charged electrode.
23
Q
In terms of vectors, what is meant by the term anti-parallel?
A
In the same line but in opposite directions.
24
Q
What is an antiparticle?
A
The antimatter counterpart of a particle, with the opposite charge to the particle and exactly the same rest mass as the particle.
25
Define "antiphase".
When particles oscillating completely out of step with each other.
26
What is the aphelion?
The furthest point from the sun in an orbit.
27
State the Archimedes principle.
The upthrust of an object in a fluid is equal to the weight of the fluid it displaces.
28
Define "Astronomical unit".
The average distance between the earth and the sun.
29
What is the atomic mass unit?
One atomic mass unit is one twelfth of the mass of carbon-12.
30
Define "Attenuation".
The decrease in intensity of electromagnetic radiation as it passes through matter and/or space.
31
What is an attenuation coefficient?
A measure of the absorption of x-ray photons by a substance.
32
Define "Average speed"
The rate of change in distance calculated over a complete journey.
33
Define "Average velocity".
The rate of change in displacement for a journey divided by the time taken.
34
What is background radiation?
The radiation emitted by the surroundings which must be measured before radiation in an experiment can usefully be measured.
35
What is a baryon?
Any hadron made with a combination of three quarks.
36
What is a base unit?
One of the seven base units that form the building blocks of the SI measurement system.
37
What is a battery?
A collection of cells that transfers chemical energy into electrical.
38
Define "becquerel".
An activity of one decay per second.
39
What is Beta decay?
A neutron in an unstable nucleus decays into a proton, electron, an electron anti-neutrino, or proton into a neutron, a positron and an electron neutrino.
40
What is Beta Radiation?
Ionising radiation consisting of fast moving electrons emitted from an unstable nucleus.
41
What is the big bang?
The theory that a moment in the universe in the past all matter in the universe was contained in a singularity, the beginning of space and time, that expanded rapidly outwards.
42
What is binding energy?
The minimum energy required to completely separate a nucleus into its constituent protons and neutrons.
43
What is the binding energy per nucleon?
The binding energy divided by the number of protons and neutrons in the nucleus; greater binding energy per nucleon, the more tightly bound the nucleons within the nucleus.
44
What is a black body?
An idealised object that absorbs all electromagnetic radiation incident on it and, when in thermal equilibrium, emits a characteristic distribution of wavelengths at a specific temperature.
45
What is a black hole?
The remnant core of a massive star after it has gone supernova and the core collapsed so far in order to escape it an object would need a greater escape velocity than the speed of light, meaning that nothing can escape it. .
46
What is blue shift?
The shortening of observed wavelength that occurs when a wave source is moving towards and observer.
47
What defines the Boltzmann constant?
A measure of the amount of energy (i.e., heat) corresponding to the random thermal motions of the particles making up a substance.
48
State Boyle's law.
The pressure of an ideal gas is inversely proportional to its volume, provided that the mass and temperature don't vary.
49
What is the braking distance of an object?
Distance travelled by the object from the time the brakes are applied unit the object comes to rest.
50
What is the breaking strength of a material?
The stress value at the point of fracture.
51
What is meant by the term brittle?
A property of material that doesn't show plastic deformation and deforms very little.
52
What is Brownian motion.
The continuous random motion of small particles suspended in a fluid, visible under a microscope.
53
Define Capacitance.
The charge stored per unit potential difference across a capacitor.
54
What is a capacitor?
A component that stores charge, consisting of two plates and an insulator.
55
What is a cathode?
A negatively charged electrode.
56
What is a cation?
A positively charged ion, which is attracted to the cathode.
57
What is a cell, in terms of electricity?
A component that transfers chemical energy to electric.
58
What is the Celsius scale?
A temperature scale with 100 degrees between the freezing point and boiling point of pure water, at atmospheric pressure.
59
What is an objects center of gravity?
An imaginary point at which the entire weight of the object appears to act.
60
What is an objects center of mass?
A point through which any external force applied produces a straight line motion with no rotation.
61
What is centripetal acceleration?
The rate of change in velocity of any object travelling in a circular path at a constant speed, which always acts towards the center the circle.
62
What is centripetal force?
A force that keeps an object travelling in a circular path at a constant speed.
63
In terms of nuclear physics, what is a chain reaction?
A reaction in which the neutrons from a previous reaction are responsible for further reactions taking place, leading to an exponential increase in the rate of reactions.
64
What is the Chandraseka's limit?
The mass of star's core beneath with the electron degeneracy pressure is sufficient to prevent gravitational collapse.
65
What is a charge carrier?
A particle with a charge that moves through a material to produce an electrical current.
66
What is a closed system?
An isolated system that has no interaction with its surroundings.
67
What is a cloud chamber?
A detector of ionising radiation consisting of a chamber filled with air saturated with vapor at low temperature so that droplets of liquid condense around the ionising particles left along the path radiation.
68
What is Coherence?
The two wave sources, or waves, have a constant phase difference.
69
What is a collimator?
Part of a gamma camera, considiting of long thin tubes that absorb any photons arriving at an angle to the axis of the tubes so that the picture is clear.
70
What is a comet?
A small, irregular body made of ice, dust and small pieces of rock in an orbit around the sun.
71
What is compression, in terms of waves?
A moving region in which the medium is denser or has higher pressure than the surrounding medium.
72
What is compressive deformation?
A change in the shape of an object due to the compressive forces.
73
What are compressive forces?
Two or more forces that have the effect of shortening or reducing the volume.
74
What is a conical pendulum?
A simple pendulum that oscillates in a horizontal circle rather than a vertical swing.
75
State the law of conservation of charge.
The electrical charge an neither be created nor destroyed in an interaction.
76
What is constructive interference?
Superposition of two waves in phase so that the resultant wave has a greater amplitude than the original waves.
77
What is a continuous spectrum?
A spectrum in which all visable frequencies/ wavelengths are present.
78
What is a control rod?
Rods made of neutron absorbing material, which ca be moved into and out of a nuclear core to ensure that exactly one neutron causes 1 reaction.
79
What is conventional current?
A model used to describe electric current in a circuit (From positive to negative).
80
What is a corrected count rate?
The radiation count rate measured in the experiment minus the background count rate.
81
State the cosmological principle.
The assumption that, when viewed on a large enough scale, the universe is homogeneous and isotropic.
82
State Coulombs law.
Any two point charges exert an electrostatic force on each other that is directly proportional to the product of their charges and inversely proportional to the square of their separation.
83
In terms of forces, what is a couple?
A pair of equal forces and opposite forces acting on a body, along the same line.
84
What is a coupling gel?
A gel with an acoustic impeadence similar to the skin it is being placed onto the transducer and the patients skin before the ultrasound scan in order to remove air pockets to ensure the most amount of ultrasound is sent into the patient.
85
What is the critical angle?
The angle of incidence at the boundary between two media that will produce an angle of refraction of 90.
86
Define the term damping.
An oscillation is being damped when an external force has the effect of reducing the amplitude of its oscillator.
87
What is dark energy?
A hypothetical form of energy that fills all of space and would explain the accelerating expansion of the universe.
88
What is dark matter?
A hypothetical form of mater spread throughout the universe that neither emits or absorbs light.
89
What is a daughter nucleus?
A new nucleus formed after radioactive decay.
90
What is a decay constant?
The probability of decay of an individual nucleus per unit time.
91
What is a derived quantity?
A quantity that comes from a combination of base units.
92
What is destructive interference?
Superposition of two waves out of phase so that the resultant wave has a lesser amplitude than the original waves.
93
What is diffraction?
When waves passing through a gap or around an obstacle the spread out.
94
What is a diffraction grating?
A glass or plastic slide on which as many as as 1000 lines per mm are rules, at a spacing that diffracts visible light.
95
What is a diode?
A semiconductor that allows current only in one direction.
96
Define Displacement.
The distance travelled in a particular direction.
97
What is a drag force?
A resistive force exerted by a fluid on an object moving through it.
98
What is the Doppler effect?
The change in the observed frequency and wavelength received from an object moving relative to the observer.
99
What is a driving frequency?
The frequency with witch a periodic force is applied to a system causing forced oscillation.
100
Define Ductile.
A property of a material that has a large plastic region in a stress-strain graph, so can be drawn into wired.
101
What is elastic deformation?
A reversible change in the shape of an object due to a compressive/ tensile force.
102
What is an elastic limit?
The point at which deformation is no longer reversible. After which plastic deformation occurs.
103
Define elastic potential energy.
The energy stored in an object due to its deformation.
104
Define electric current.
The rate of flow of charge.
105
What is electric field strength, at a point?
The force exerted per unit positive charge at a point in the electric field.
106
What is electrical potential?
The work done by an external force per unit positive charge to bring the charge from infinity to that point in the field.
107
What is electrical potential difference?
The difference in work done completed by an external force to move a positive charge from one point to another.
108
What is the electromagnetic spectrum?
The full range of electromagnetic waves organised by their frequencies.
109
What is an electromagnetic wave?
Transverse waves with oscilatig electric and magnetic field properties. meaning they don't need a medium to travel trough.
110
What is an E.M.F?
The energy transferred from chemical to electrical energy per unit charge.
111
What id electron degeneracy pressure?
A quantum-mechanical pressure created by electrons in the core of a collapsing star explained by the Pauli extension principle.
112
What is an electron gun?
A device that uses a large potential difference to produce a narrow beam of electrons.
113
What is an emission line spectrum?
A set of specific frequencies of electromagnetic radiation, visible as bright lines in spectroscopy, emitted by excited electrons as they make transitions between energy states.
114
Define energy.
The capacity for doing work.
115
What is an energy level?
A discrete amount of energy that an electron within an atom is permitted to poses.
116
Define escape velocity.
The minimum velocity at which an object has just enough energy to leave a specified gravitational field.
117
What is mean when an atom is excited?
An atom containing electron (s) that have absorbed energy move onto a higher energy level.
118
State the idea of the expanding universe.
The idea that the fabric of space and time is in all firections and that as a result any point, in any part of the universe, is moving away from every other point in the universe.
119
What is exponetial decay?
A constant-ration process in which quantity decreases by the same factor in equal time intervals.
