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Definitions Flashcards

1
Q

Vector

A

A physical quantity with magnitude and direction

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2
Q

Scalar

A

A physical quantity with magnitude only

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3
Q

Moment

A

Force times perpendicular distance from the line of action of the force to the point

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4
Q

Principle of moments

A

For an object in equilibrium, the sum of the clockwise moments is equal to the sum of the anticlockwise moments about any point

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5
Q

Couple

A

A pair of equal and opposite forces acting on a body, but not along the same line

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6
Q

Velocity

A

Change of displacement per unit time

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7
Q

Acceleration

A

Change of velocity per unit time

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8
Q

Newton’s 1st Law

A

An object will remain at rest or at a constant velocity unless acted on by an external resultant force

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9
Q

Newton’s 2nd Law

A

The force is proportional to the rate of change of momentum

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10
Q

Newton’s 3rd Law

A

For every action there is an equal and opposite reaction

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11
Q

Equilibrium

A

State of an object when at rest or moving at constant velocity

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12
Q

Density

A

Mass per unit volume of the substance

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13
Q

Stress

A

Force per unit area of cross section in a solid perpendicular to the cross section

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14
Q

Strain

A

Extension per unit length of a solid when deformed

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15
Q

Young’s Modulus

A

Tensile stress/strain

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16
Q

Limit of Proportionality

A

The limit beyond which, when a wire or a spring is stretched, its extension is no longer proportional to the force that stretches it

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17
Q

Plastic deformation

A

Deformation of a solid beyond its elastic limit, the object will not return to its original length once the force is removed.

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18
Q

Elastic limit

A

Point beyond which a wire is permanently stretched

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19
Q

Hooke’s Law

A

The extension of a spring is directily proportional to the force applied to it, up to the limit of proportionality

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20
Q

Isotope

A

Atoms with the same number of protons but different numbers of neutrons

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21
Q

Conservation of energy

A

Energy cannot be created or destroyed, only converted from one form to another

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22
Q

Work done

A

Force times distance moved in the direction of the force

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23
Q

Ductile

A

Material that can be drwan into threads, it can be shaped or permanently deformed without fracture

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24
Q

Brittle

A

Material cannot be permanently stretched

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25
Wave
Transfer energy from A to B via a medium of transfer, without transferring the medium
26
Standing wave
When two waves travel in opposing directions and they have the same wave speed, frequency and in general amplitude, they will superpose and form a standing wave
27
Monochromatic
Single wavelength
28
Coherent
No change in phase relationship
29
Diffraction
Spreading out or bending of waves as they pass through a gap or around an obstacle
30
Emf
Describes the amount of energy that is converted from one form to electrical and placed on a unit of charge at the source
31
Ohm's Law
The current flowing through a metallic conductor is directly proportional to the potential difference across its ends, provided the temperature remains constant
32
Resistivity
The resistance of a piece of wire 1m in length and with a cross sectional area of 1m^2
33
Centre of mass
The point through which a single force on the body has no turning effect
34
Principle of conservation of linear momentum
The total linear momentum of a system of interacting bodies is constant, providing no external forces act
35
Work function
Minimum energy to liberate electron
36
Excitation
When an electrion takes in energy from a photon or collision and goes up an energy level
37
Ionisation
When an electron takes in enough energy to leave the atom
38
Progressive waves
Waves that move outwards from their source
39
Transverse waves
Each particle oscillates perpendicular to the direction of propagation to the wave
40
Longitudinal wves
Each particle oscillates parallel to the direction of propagation to the wave
41
Rarefied
More distance between particles than usual
42
Compression
Particles closer together
43
Mechanical waves
Oscillation of particles in a physical medium
44
Refraction
Change in path of light ray caused by a change in speed
45
Total internal reflection
The angle of incidence is greater than the critical angle
46
Diffraction
The spreading of waves when passed through a gap or round an obstacle
47
Kirchhoff's First Law
The sum of the currents leaving any junction is always equal to the sum of the currents that entered it
48
Kirchhoff's Second Law
The sum of potential differences across components of a series circuit is equal to the emf
49
Internal Resistance
Resistance inside a source of electrical energy; the loss of pd per unit current in the source when current passes through it
50
Potential Divider
Two or more resistors in series connected to a source of pd
51
Superconductor
A material that has zero electrical resistance below a critical temperature.
52
Gravitational Field Strength
The force per unit mass acting on a small test mass placed in the field
53
Gravitational Potential
The work done to move a unit mass from infinity to that point in a gravitational field
54
Kepler's First Law
All planets move about the Sun in elliptical orbits, having the Sun as one of the foci
55
Kepler's Second Law
A radius vector joining any planet to the sun, sweeps out equal areas in equal lengths of time
56
Kepler's Third Law
The square of the period of a planet's orbit is proportional to the cube of the mean radius of its orbit
57
Coulomb's Law
The magnitude of the force between two charges is proportional to the product of the charges and inversely proportional to the square of the distance between them
58
Electric Field
Region where a charged particle will experience a force
59
Gravitational Field
The region surrounding an object in which it exerts a gravitational force on any other object
60
Geostationary Satellite
A satellite that stays above the same point on the Earth's equator as it's period is 24 hours and has the same rotation direction
61
Electric Field Strength
Force per unit charge acting on a small positive test charge at a point in the field
62
Electric Potential
Work done per unit positive charge moving a small positive charge from infinity to that point in the field
63
Field
A region around an object where a force is exerted
64
Capacitance
The charge stored per unit pd of a capacitor
65
Dielectric
Material that increases the capacity of a parallel-plate capacitor to store charge when placed between the plates of the capacitor
66
Activity
The number of unstable radioactive nuclei that decay per second
67
Metastable State
An excited state of the nuclei of an isotope that last long enough after α or β emission for the isotope to be separated from the parent isotope
68
Atomic Mass Unit
One twelfth of the mass of a carbon-12 atom
69
Mass Defect
Mass of separated nucleons minus mass of nucleus
70
Binding Energy
The work that must be done to separate a nucleus into its constituent nucleons
71
Critical Mass
The minimum mass required to sustain a chain reaction of fission in a nuclear reactor
72
Fuel Rods (Nuclear Reactor)
Contains enriched uranium. Increased % of U-235 compared to uranium ore it's extracted from
73
Control Rods (Nuclear Reactor)
Made of cadmium or boron to absorb neutrons | Lifted in and out of the reactor to control the number of neutrons present and the rate of fission
74
Moderator (Nuclear Reactor)
Made of graphite or water | Slows down fission neutrons into one thermal energies, to increase the likelihood of absorption by U-235 nuclei
75
Coolant (Nuclear Reactor)
Water flows around the core, transferring heat away from the fuel, to be used to produce steam to drive a turbine
76
Angular Displacement
The angle moved through relative to a specific axis
77
Angular Velocity
The rate of change of angular displacement with respect to time
78
Centripetal Force
The force that makes an object move in a circle
79
Simple Harmonic Motion
Acceleration is proportional to the displacement of the object from equilibrium and is always directed towards the equilibrium position
80
Natural Frequency
The frequency of free oscillations of an oscillating system
81
Free Vibrations
Vibrations where there is no damping and no periodic force acting on the system, so the amplitude of the oscillations is constant
82
Forced Vibrations
Vibrations of a system subjected to an external periodic force
83
Resonance
The driving force matches the natural frequency of the system, leading to an increased amplitude of oscillation
84
Damping
The removal of energy from an oscillating system
85
Magnetic Flux Density
The magnetic force per unit length per unit current on a current carrying conductor at right angles to the field lines
86
Electromagnetic Induction
The generation of an emf when the magnetic flux linkage through a coil changes or a conductor cuts across magnetic field lines
87
Lenz's Law
The direction of the induced emf is always such as to oppose the change that causes the emf
88
Hall Probe
A device used to measure magnetic flux density
89
Magnetic Flux
The product of magnetic flux density and the area perpendicular to the field
90
Magnetic Flux Linkage
A measure of the magnetic flux of a coil of wire
91
Faraday's Law of Electromagnetic Induction
The induced emf in a circuit is equal to the rate of change of magnetic flux linkage through the circuit
92
Eddy Current
Induced currents in the metal parts of machines
93
Internal Energy
Sum of Ep and Ek of molecules within the body
94
Boyle's Law
When a fixed mass of gas is reduced in volume by a compressing piston, the pressure inside the piston increases
95
Charles' Law
For the fixed mass of an ideal gas at constant pressure, its volume is directly proportional to its absolute temperature
96
Ideal Gas
A gas under conditions such that it obeys Boyle's Law

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