All Definitions Flashcards
(115 cards)
1
Q
Work done/energy transferred
A
Product of the force and the distance moved by the force in the direction of movement.
2
Q
One Joule (J)
A
Is transferred when a force on 1N causes an object to move a distance of 1 metre in the direction of the force.
3
Q
Energy (E)
A
The capacity to do work (J)
4
Q
A closed system
A
Any system in which all the energy transfers are accounted for. Energy or matter cannot enter or leave a closed system.
5
Q
The principle of conservation of energy
A
The total energy of a closed system remains constant. Energy can neither be created or destroyed, it can only be transferred from one form to another.
6
Q
Gravitational potential energy
A
Energy an object has because of its position.
7
Q
Power
A
Rate of doing work (the rate at which energy is transferred from one form to another)
8
Q
Newton’s first law
A
A body will remain at rest or continue to move in a straight line at a constant velocity unless an external force acts on it.
9
Q
Newton’s second law
A
The resultant force on an object is proportional to the rate of change of momentum of the object, and the momentum change takes place in the direction of the force.
10
Q
Newton’s third law
A
If object A exerts a force on object B, then object B will exert an equal and opposite force on object A.
11
Q
The principle of conservation of momentum
A
Total momentum before a collision is always equal to the total momentum after the collision, provided that no external forces are involved.
12
Q
Impulse
A
Product of a force F and the time ∆t for which the force acts.
13
Q
Net force
A
Rate of change of momentum.
14
Q
Elastic collision
A
Collision in which momentum and kinetic energy are conserved- no energy is transferred to other forms such as heat/sound.
15
Q
Inelastic collision
A
Momentum is conserved but some of the kinetic energy is transferred into other forms in the collision.
16
Q
Electromotive force
A
E.m.f of a supply is the energy gained per unit charge by charges passing through a supply, when a form of energy is transferred to electrical energy carried by the charges. (V or JC^-1)
17
Q
Protons
A
Positively charged particles.
18
Q
Electric current
A
Rate of flow of charge.
19
Q
Electrolyte
A
A fluid that contains ions that are free to move and hence conduct electricity.
20
Q
Kirchoff’s first law
A
The sum of the currents entering any junction is always equal to the sum of currents leaving the junction (conservation of charge).
21
Q
One coulomb
A
Quantity of charge that passes a fixed point in one second when a current of one ampere is flowing (1C=1As).
22
Q
Conductor
A
Material with high number density of conduction electrons and therefore a low resistance.
23
Q
Semiconductor
A
Material with lower number of conduction electrons than a conductor and therefore a higher resistance.
24
Q
Insulator
A
Material with a small number density of conduction electrons and therefore a very high resistance.
25
Potential difference (p.d)
Measured across a component is the energy transferred per unit charge by the charges passing through the component. (V or JC^-1)
26
Kinetic energy
The work an object can do by virtue of its speed, measured in J (scalar).
27
Electronvolt
The kinetic energy gained by an electron when it is accelerated through a p.d of 1 volt.
28
Ohms law
Current through a conductor is directly proportional to the p.d across it, provided that physical conditions, such as temperature remain constant.
29
Resistance
Property of a component that regulates the electric current through it (Ω).
(Measure of the opposition of the metal to the flow of current through it)
30
Resistivity
Ratio of the product of resistance and cross-sectional area of a component and it’s length.
31
Kirchoff’s second law
In any closed loop, the sum of e.m.f is equal to the sum of the products of current and the resistance (consequence of conservation of energy).
32
Potential divider
A type of circuit containing two components designed to divide up the p.d in proportion to the resistances of the components.
33
A potential divider circuit
Uses two resistors in series to split or divide the voltage of the supply in a chosen ratio so that a chosen voltage can be provided to another device or circuit.
34
Terminal p.d
The p.d recorded across the terminals of a cell. The difference between the e.m.f and the terminal p.d when charge flows in the cell is called lost volts.
35
Internal resistance, r
Resistance to electric current of the materials inside (chemicals, power source wires or components). When a current flows, energy is transferred to these materials resulting in the terminal p.d dropping.
36
Fiducial mark
An object placed in the field of view for the observer to use as a point of reference.
37
Anomalous
Values in a set of results do not fit the overall trend in the data and so are judged not to be part of the inherent variation.
38
Random errors
Measurements that are scattered randomly above and below the true value when the measurement is repeated. Find mean of several reading for better results.
39
Systematic error
Error that doesn’t happen by chance but instead is introduced by an inaccuracy in the apparatus or it’s use by the person conducting the investigation. This type of error tends to shift all measurements in the same direction.
40
Zero error
Type of systematic error caused when an instrument is not properly calibrated or adjusted, and so gives a non-zero value when the true value is zero.
41
Precision
Degree to which repeated values, collected under the same conditions in an experiment, show the same results.
42
Accuracy
Degree to which a value obtained by an experiment is close to the actual or true value.
43
Scalar
Quantity magnitude with no direction.
44
Vector
Quantity magnitude and direction.
45
Displacement, x
Distance moved by an object from its equilibrium (or rest) position; may be positive or negative.
46
Components of a vector
Parts of a vector in 2 perpendicular directions. The process is called resolving the vector.
47
Acceleration
Rate of change of velocity.
48
Thinking distance
Distance a car travels between the driver seeing the hazard and applying the brakes.
49
Braking distance
Distance car travels between applying the brakes and coming to rest.
50
Resultant force
Single force which has the same effect as the sum of all the forces acting on a body.
51
One Newton
Force that causes a mass of 1kg to have an acceleration of 1m/s^2.
52
Tension
Force experienced by any rope, string, cable or wire that has been pulled, hung, rotated or supported.
53
Normal contact force/reaction force
Force that acts perpendicular to the point of contact of a body and the surface with which is in contact.
54
Upthrust
Upwards force that liquid/gas exerts on a body floating in it due to the water displaced.
55
Friction
Force between two surfaces in contact with one another and is caused by interatomic and intermolecular forces when surfaces are in contact. Friction opposes motion at the point of contact.
56
Drag
Frictional force experienced by an object travelling through the fluid. The effect of drag is always to oppose the motion taking place.
57
Terminal velocity
Velocity at which an object’s drag equals it’s accelerating force. Therefore there is no resultant force and zero acceleration.
58
Equilibrium
Objects are in equilibrium when all the forces acting on them in the same plane (coplanar forces) are balanced - there is zero net or resultant force. In terms of motion, the object is either stationary or travelling at constant velocity.
59
Triangle of forces
Represents the direction and magnitude of 3 coplanar forces that are acting on an object in equilibrium.
60
Zero resultant force
Zero acceleration for an object and such an object is said to be in equilibrium.
61
The moment of a force/turning moment
Product of a force and the perpendicular distance of its line of action from the point or axis.
62
The principle of moments
For an object to be in rotational equilibrium, the sum of the clockwise moments must equal the sum of the anti-clockwise moments.
63
The turning moment (torque) due to a couple
The product of one of the forces and the perpendicular distance between them (Nm).
64
Couple
When 2 equal, anti parallel forces act to produce a rotation- no linear motion occurs.
65
Centre of mass
Single point at which all the mass of the object can be assumed to be situated. For a symmetrical body of constant density, this will be at the centre of the object.
66
Nuclear fusion
The process of two nuclei joining together and releasing energy from a change in binding energy.
67
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 own mass.
68
Radiation pressure
Due to the momentum of photons released in fusion reactions, and acts outwards (in the direction of energy flow).
69
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=1/3Nmc^2. Gas pressure acts in all directions at a point inside a gas, such as inside a star.
70
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 star’s luminosity against temperature (Hertzsprung-Russell diagram).
71
Red giant
A star in the 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 it’s surface layers have cooled and expanded.
72
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.
73
Planetary nebula
An expanding, glowing shell of ionised hydrogen and helium ejected from a red giant star at the end of its life.
74
Electron degeneracy pressure
The pressure that stops the gravitational collapse of a low-mass star (below the Chandrasekhar limit of 1.4 solar masses). This is the pressure that prevents a white dwarf star from collapsing.
75
Chandrasekhar limit
The maximum possible mass for a stable white dwarf star and is equal to 1.4 times the mass of our sun. White dwarfs with masses above this will collapse further to become neutron stars or black holes.
76
Red super giant
A star that has exhausted all the hydrogen in its core and has a mass much higher than the Sun.
77
Supernova
A huge explosion produced when the core of a red super giant collapses.
78
Neutron star
The remains of the core of a red super giant after it has undergone a supernova explosion. It is incredibly dense and composed mainly of neutrons.
79
Black hole
The core of a massive star that has collapsed almost to a point. Black holes are very dense and very small, with a gravitational field so strong that light cannot escape (the escape velocity is greater than the speed of light).
80
Hertzsprung-Russell (HR) diagram
A luminosity-temperature graph.
81
Luminosity
The luminosity of a star is the total energy that the star emits per second.
82
Continuous spectrum
A spectrum that appears to contain all wavelengths over a comparatively wide range.
83
Energy levels
Energy levels inside an atom are 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.
84
The emission line spectrum
The emission line spectrum of an element is 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 consists of a series of bright lines against a dark background.
85
An absorption line spectrum
The pattern of dark lines in a continuous spectrum from a light source and is caused by light passing through an absorbing medium such as gas. The dark lines represent the wavelengths that are absorbed.
86
A transmission diffraction grating
A glass surface having a large number of very fine parallel grooves or slits, and used to produce optical spectra by diffraction of transmitted light.
87
Maxima
Regions of brightness which will be seen when the path difference between overlapping waves is equal to a whole number of wavelengths, i.e. nλ=dsinθ, where n=1,2,3…
88
Wien’s displacement law
States that λmax ∝ 1/T or λmaxT= constant (2.89x10^-3m K), where T is temperature on the absolute (Kelvin) scale. It is used to estimate the peak surface temperature of a star from the wavelength at which the star’s brightness is maximum.
89
Stefan’s law
Relates the luminosity L of a star (The radiation flux emitted from the surface of a star) with its absolute temperature T: L= 4πr^2σT^4 where the constant, σ, is known as Stefan’s constant and has a value of 5.67x10^-8 Wm^-2K^-4.
90
The astronomical unit (AU)
The mean distance from the centre of the Earth to the centre of the Sun.
91
Parsec
A unit of distance that gives a parallax angle of one second of arc (1/3600 of a degree), using the radius of the Earth’s orbit (1 AU) as the baseline of a right-angled triangle. 1 parsec is approximately equal to 3.1x10^16.
92
Stellar parallax
Is the apparent shifting in position of a star viewed against a background of distant stars when viewed from different positions of the Earth, such as different positions of the Earth’s orbit around the Sun.
93
Light-year
The distance travelled by light in one year. One light-year is approximately equal to 9.5x10^15m.
94
The Doppler effect or Doppler shift
The change in wavelength caused by the relative motion between the wave source and an observer. For electromagnetic radiation of frequency f and wavelength λ, the Doppler equation is Δλ/λ ≈ Δf/f ≈ v/c where c is the speed of light.
95
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.
96
Hubble’s law
States that the recessional velocity, v, of a galaxy is directly proportional to its distance, d, from the Earth.
97
The Hubble constant H_0
The constant of proportionality in the equation  v ≈ H0d. The SI unit for H0 is s^-1, but it can also be quoted in kilometres per second per megaparsec (kms^-1Mpc^-1).
98
Cosmic microwave background radiation (CMBR)
Microwave radiation received from all over the sky originating from after the Big Bang, when the universe had cooled to a temperature near 3000 K. As the universe has expanded this radiation is now just a faint microwave glow with a peak wavelength corresponding to a temperature of 2.7 K (the same as the temperature of the universe).
99
The 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 creation, 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.
100
The cosmological principle
States that on a large scale the universe is isotropic (the same in all directions) and homogenous (of uniform density as long as large enough volume is considered).
101
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.
102
Dark energy
A type of energy that permeates the whole universe and opposes the attractive force of gravitation between galaxies by 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.
103
Amplitude, x_0
The maximum displacement (will always be positive).
104
Frequency, f
The number of oscillations per unit time at any point.
105
Period, T
Time taken for one complete pattern of oscillation at any point.
106
Angular frequency, ω
The product 2πf or alternatively ω= 2π/T (unit of rads^-1).
107
Phase difference,ϕ
The fraction of a complete cycle or oscillation between two oscillating points, expressed in degrees or radians.
108
Simple harmonic motion
A body will oscillate with simple harmonic motion if it’s acceleration is directly proportional to its displacement from a fixed point and always directed towards that fixed point.
109
Isochronus
The period of an object with SHM is isochronus; this means that it is constant and independent of the amplitude of the oscillation.
110
Damping
Forces reduce the amplitude of an oscillation with time, due to energy being removed from the oscillating system.
111
Free oscillations
Occur when there is no external, periodic force. The system oscillates at its natural frequency.
112
Natural frequency
The frequency at which a system will oscillate when undergoing free oscillations.
113
Forced oscillations
Occur when an external force or driving force is applied to keep the body oscillating. The system oscillates at the frequency of the driving force that is causing the oscillations.
114
Driving frequency
The frequency of the driving force applied to an oscillating object.
115
Resonance
Forced oscillations occurs when the driving frequency is equal to the natural frequency of the system being forced to oscillate. This results in the body oscillating at its natural frequency and maximum amplitude.
