Download Physics 12 – Important Terms

Physics 12 – Important Terms
Basics Terms: Physics and Physical Measurement
1. Fundamental Units – seven basic units of the SI measurement system: kilogram, second, mole, meter, ampere, Kelvin, candela.
2. Derived Units – units that are combinations of fundamental units. These combinations may or may not have a separate name. (eg. 1 kg
m/s2 = 1 N)
3.
Accuracy - An indication of how close a measurement is to the accepted value (a measure of correctness).
4.
Precision - An indication of the agreement among a number of measurements made in the same way (a measure of exactness).
5.
Vector – a quantity with both a magnitude and a direction
6.
Scalar – a quantity with magnitude only
7.
Displacement (d) - distance traveled from a fixed point in a particular direction
8.
Velocity (v) - rate of change of displacement
9.
Speed (u) - rate of change of distance
10. Acceleration (a) - rate of change of velocity
Chapter 12: Gravitation & Fields
11. Newton’s Universal Law of Gravitation – The force of gravity between two objects is directly proportional to the product of the two
masses and inversely proportional to the square of the distance between them and acts along a line joining their centers. (NOTE: The
objects are point masses. If they are not point masses but are very far apart, that is, the distance between them is very much greater than
their radii, they can be treated like point masses.)
12. Gravitational Field Strength (g) – gravitational force per unit mass exerted on a small or point mass (g = F g / m)
13. Gravitational Potential Energy (EP) - the work done bringing a small point mass in from infinity to a point in a gravitational field
(NOTE: the work done is path independent)
14. Gravitational Potential (V) – the work done per unit mass bringing a small point mass in from infinity to a point in a gravitational field
(NOTE: the work done is path independent)
15. Equipotential Surface – a surface on which the potential is the same everywhere
16. Escape Speed (vesc ) – minimum speed an object must have at the surface of a planet in order to escape the gravitational field of the planet
17. Kepler’s Third Law - the ratio of the orbital period squared to the average orbital radius cubed is constant for all planets
18. Weightlessness in free-fall – a sensation of weightlessness because a person is falling freely toward the Earth, hence there is no normal
force (reaction force) acting on the person due to gravity
19. Weightlessness in orbital motion – a sensation of weightlessness due to the spacecraft and all objects in it being in constant free-fall
together as they circle Earth
20. Weightlessness in deep space – a sensation of weightlessness due to the minimal pull of gravity very far from any massive object
Chapter 13 - 14: Fundamentals of Electricity
21. Field (Field of Force) – a region of space where a mass or charge experiences a force
22. Law of Conservation of Electric Charge – The total electric charge of an isolated system remains constant.
23. Conductor – material through with electric charge flows freely
24. Insulator – material through which electric charge does not flow freely
25. Coulomb’s Law – The electric force between two point charges is directly proportional to the product of the two charges and inversely
proportional to square of the distance between them, and directed along the line joining the two charges. (F = k q1 q2 / r2)
26. Insulator – material through which electric charge does not flow freely
27. Electric Field Strength (E) - Electric force per positive unit test charge (E = F/q)
28. Radial Field – field that extends radially (like the electric field around a point charge or the gravitational field around a planet)
29. Electric Potential (V) - work done per unit charge moving a small positive test charge in from infinity to a point in an electric field. (V =
W/q) (V = kq/r) (NOTE: the work done is path independent)
30. Electric Potential Energy (Ee)- energy that a charge has due to its position in an electric field
31. Electric Potential Difference (ΔV) – electric potential energy difference per unit charge between two points in an electric field (ΔV = ΔE e
/ q OR ΔV = W / q)
32. Electronvolt (eV) – energy gained by an electron moving through an electric potential difference of one volt. (OR: Work done moving an
electron through an electric potential difference of one volt.) (1 eV = 1.60 x 10 -19 J)
33. Magnitude of a Magnetic Field (magnetic field strength, magnetic field intensity, magnetic flux density) (B) – ratio of magnetic force
on a current carrying conductor to the product of the current and length of wire and sine of the angle between the current and the magnetic
field (B = FB / Ilsinθ) (OR: ratio of magnetic force on a charged particle to the product of the charge and its velocity and the sine of the
angle between the velocity and the magnetic field) (B = FB / qvsinθ)
34. Direction of a Magnetic Field – the direction that the North pole of a small test compass would point if placed in the field (N to S)
Chapter 15: Electric Circuits
35. Electric Current (I) – current is defined in terms of the force per unit length between parallel current-carrying conductors (NOTE: one
ampere of current is the amount of current in each of two infinitely long straight wires one meter apart experiencing a magnetic force per
unit length of 2 x 10-7 newtons)
36. Resistance (R) - ratio of potential difference applied across a piece of material to the current through the material (R = V/I)
37. Resistor - device with a constant resistance (Ohmic device) over a wide range of potential differences
38. Ohm’s Law – For a conductor at constant temperature, the current flowing through it is proportional to the potential difference across it
(NOTE: R = V/I is not a statement of Ohm’s Law)
39. Electromotive Force (emf) (ε) - total energy per unit charge supplied by the battery around a circuit (ε = ΔE e/q
OR ε = W/q)
40. Internal Resistance (r) – the resistance supplied by the materials within the device (eg. battery or meter)
41. Ideal Ammeter – one with zero internal resistance – must be placed in series
42. Ideal Voltmeter – one with infinite internal resistance – must be placed in parallel
Chapter 16: Fundamentals of Electromagnetism
43. Magnetic Flux (Φ) - product of the magnetic field strength and a cross-sectional area and the cosine of the angle between the magnetic
field and the normal to the area (Φ = B A cosθ)
44. Magnetic Flux Linkage – product of the magnetic flux through a single coil and the total number of coils (flux linkage = N Φ)
45. Faraday’s Law - The emf induced by a time changing magnetic field is proportional to the rate of change of the flux linkage. (ε α N
ΔΦ/Δt)
46. Lenz’s Law - The direction of an induced emf is such that it produces a magnetic field whose direction opposes the change in magnetic
field that produced it. (NOTE: This is the negative sign added to Faraday’s law. ε= - N ΔΦ/Δt)
47. Root Mean Square (rms) Value of an Alternating Current (or Voltage) – the value of the direct current (or voltage) that dissipates
power in a resistor at the same rate (NOTE: The rms value is also known as the “rating.”)
Chapter 18 - 19: Introduction to Quantum Physics
48. Photon – a discrete unit or package of light energy
49. Photoelectric Effect - the emission of electrons from a metal when electromagnetic radiation of high enough frequency falls on the
surface
50. Threshold Frequency (f0) - minimum frequency of light needed to eject electrons from a metal surface
51. Work Function (Φ) - minimum energy needed to eject electrons from the surface of a metal
52. Millikan’s Stopping Potential Experiment – an experiment utilizing reverse voltage raised to such a level (stopping potential V s) that it
stops all emitted photoelectrons (NOTE: This experiment is used to test the Einstein model of the explaining the photoelectric effect.)
53. De Broglie Hypothesis - All particles can behave like waves whose wavelength is given by λ = h/p where h is Planck’s constant and p is
the momentum of the particle.
54. Matter Waves - All moving particles have a “matter wave” associated with them whose wavelength is the de Broglie wavelength.
55. Wave-Particle Duality: Both matter and radiation have a dual nature. They exhibit both particle and wave properties.
56. Schrödinger Model of the Atom – This model assumes that electrons in the atom may be described by wavefunctions. The electron has
an undefined position, but the square of the amplitude of the wavefunction gives the probability of finding the electron at a particular point.
57. Heisenberg Uncertainty Principle – Conjugate quantities (position-momentum or time-energy) cannot be known precisely at the same
time. (NOTE: There is a link between the uncertainty principle and the de Broglie hypothesis. For example, if a particle has a uniquely
defined de Broglie wavelength, then its momentum is known precisely but all knowledge of its position is lost.)
Chapter 20 - 21: Introduction to Atomic and Nuclear Physics
58. Geiger-Marsden experiment – also known as the Rutherford Alpha Particle Scattering or Gold Foil Experiment
59. Bainbridge Mass Spectrometer – a device used to determine atomic masses – consists primarily of a velocity selector and a magnetic
chamber
60. Nuclide – a particular type of nucleus with a certain number of protons and neutrons
61. Isotope - nuclei with the same number of protons (Z) but different number of neutrons (N)
62. Nucleon – a proton or neutron (NOTE: Do not say “a particle in the nucleus” since that would include quarks as well.)
63. Nucleon Number (Mass Number) (A) - number of nucleons (protons + neutrons) in nucleus
64. Proton Number (Atomic Number) (Z) - number of protons in nucleus
65. Neutron Number (N) - number of neutrons in nucleus (N = A – Z)
66. Radioactive Decay – when an unstable nucleus emits a particle (alpha, beta, gamma) (NOTE: Radioactive decay is both a random and a
spontaneous process.) (NOTE: The rate of radioactive decay decreases exponentially with time.)
67. Alpha Particle (α)– helium nucleus (2 protons + 2 neutrons)
68. Beta Positive Particle (β+) – electron
69. Beta Negative Particle (β-) – positron (antielectron)
70. Gamma Radiation (γ) – high energy (high frequency) electromagnetic radiation
71. Radioactive Half-life (T1/2) –
1) the time taken for ½ the number of radioactive nuclei in sample to decay
2) the time taken for the activity of a sample to decrease to ½ its initial value
72. Unified Atomic Mass Unit – 1/12th the mass of a carbon-12 nucleus
73. Mass Defect – difference between the mass of the nucleus and the sum of the masses of its individual nucleons
74. Binding Energy – energy released when a nuclide is assembled from its individual components (OR: energy required when nucleus is
separated into its individual components)
75. Binding Energy per Nucleon - energy released per nucleon when a nuclide is assembled from its individual components (OR: energy
required per nucleon when nucleus is separated into its individual components)
76. Nuclear Fission - a heavy nucleus splits into two smaller nuclei of roughly equal mass
77. Nuclear Fusion - two light nuclei join to form a heavier nuclei (NOTE: This is the main source of the Sun’s energy.)
78. Radioactive Decay Law –
1) The rate at which radioactive nuclei in a sample decay (the activity) is proportional to the number of radioactive nuclei
present in the sample at any one time. (A = λN)
2) N = N0e-λt OR A = λ N0e-λt (as an exponential function)
79. Decay Constant (λ) –
1) constant of proportionality between the decay rate (activity) and the number of radioactive nuclei present
2) probability of decay of a particular nuclei per unit time
80. Second Law of Thermodynamics – Thermal energy may be completely converted to work in a single process, but that continuous
conversion of this energy into work requires a cyclical process and the transfer of some energy from the system.
81. Chain Reaction – neutrons released from one fission reaction go on to initiate further reactions (NOTE: Only low-energy neutrons (≈ 1
eV) favor nuclear fission.)
82. Critical Mass – minimum mass of radioactive fuel block needed for a chain reaction to occur
83. Controlled Nuclear Fission – used for power production
84. Uncontrolled Nuclear Fission – used for nuclear weapons
85. Fuel Enrichment – process by which the percentage composition of a desirable radioactive nuclide (eg. – uranium-235) is increased in
order to make nuclear fission more likely
86. Moderator – Most neutrons released in fission are fast neutrons, so a moderator is used to reduce their energy down to thermal levels to
ensure that the fission is self-sustaining. (eg. – may be made of solid graphite or steam)
87. Control Rods – are used to remove any excess neutrons to ensure the fission reaction continues safely (eg. – may be made of cadmium or
boron steel)
88. Heat Exchanger – This allows the nuclear reactions to occur in a place that is sealed off from the rest of the environment. Reactions
increase temperature in the core and this thermal energy is transferred to water and the steam that is produced turns the turbines.