87 “Phacts” for the Physics Regents Exam

(As adapted from several sources, beginning with Jim Davidson, Physics Teacher)

I. Mechanics

1. Mass and inertia are the same thing. (Mass actually measures inertia – in kilograms… Much as monetary resources measures financial wealth – in dollars.)

dog_cheating_cat_school_test_hg_clr 2. Weight (force of gravity) decreases as you move away from the earth by distance squared. (It decreases, but only approaches zero, never reaching it, even far beyond the solar system.)

3. Weight (in newtons) is mass * acceleration (w = mg). Mass is not Weight! Mass is a scalar and measured in kilograms, weight is a force and a vector and measured in Newtons.

4. Velocity can only be constant when the net force (and acceleration) is zero. (The velocity can be zero and not constant – for example when a ball, thrown vertically, is at the top of its trajectory.)

5. Velocity, displacement [s], momentum, force (weight), torque, and acceleration are vectors.

6. Speed, distance [d], time, length, mass, temperature, charge, power and energy (joules) are scalar quantities.

7. The slope of the distance-time graph is velocity.

8. The slope of the velocity-time graph is acceleration.

9. The area under a velocity-time graph is distance.

10. Magnitude is a term used to state how large a vector quantity is.

11. At zero (0) degrees two vectors have a resultant equal to their sum. At 180 degrees two vectors have a resultant equal to their difference. From the minimum value (at 180) to the maximum value (at zero) is the total range of all the possible resultants of any two vectors.

12. An unbalanced force must produce an acceleration and the object cannot be in equilibrium.

13. If an object is not accelerating, it is in equilibrium and no unbalanced forces are acting.

14. The equilibrant force is equal in magnitude but opposite in direction to the resultant vector.

15. Momentum is conserved in all collision systems. Energy is conserved (in the KE of the objects) only if a collision is perfectly elastic.

II. Energy

16. Mechanical energy is the sum of the potential and kinetic energy.

17. UNITS: a = [m/sec2];  F = [kg•m/sec2] = Newton;  work = PE = KE = [kg•m2/sec2] = Joule; Power = [kg•m2/sec3] = [Joules/sec] = Watt

18. 1ev is a very small energy unit equal to 1.6 x 10-19 joules – used for small objects like electrons. This is on the Reference Table.

19. Gravitational potential energy increases as height increases.

20. Kinetic energy changes only if mass or velocity changes.

21. Mechanical energy (PE + KE) does not change for a free falling mass or a swinging pendulum. (when ignoring air friction)

III. Electricity and Magnetism

22. A coulomb is charge, an amp is current [coulomb/sec] and a volt is potential difference [joule/coulomb].

23. Short, fat, cold wires make the best conductors.

24. Electrons and protons have equal amounts of charge (1.6 x 10-19 coulombs each – known as one elementary charge). This is on the Reference Chart.

25. Adding a resistor in series increases the total resistance of a circuit.

26. Adding a resistor in parallel decreases the total resistance of a circuit.

27. All resistors in series have equal current (I).

28. All resistors in parallel have equal voltage (V).

29. If two similar charged spheres touch each other add the charges and divide by two to find the final charge on each sphere after they are separated.

30. Insulators contain no electrons free to move.

31. Ionized gases conduct electric current using positive ions, negative ions and electrons.

32. Electric fields all point in the direction of the force on a positive test charge.

33. Electric fields between two parallel plates are uniform in strength except at the edges.

34. Millikan determined the charge on a single electron using his famous oil-drop experiment.

35. All charge changes result from the movement of electrons not protons. (an object becomes positive by losing electrons)

36. The direction of a magnetic field is defined by the direction a compass needle points. (The direction an isolated north pole would feel.)

37. Magnetic fields point from the north to the south outside the magnet and south to north inside the magnet.

38. Magnetic flux is measured in webers.

39. Left hands are for negative charges and reverse answer for positive charges.

40. The first hand rule deals with the B-field around a current bearing wire, the second hand rule deals with the magnetic field from a wire around a solenoid, and the third hand rule looks at the force on charges moving in a B-field.

41. Solenoids are stronger with more current or more wire turns or adding a soft iron core.

IV. Wave Phenomena

42. Sound waves are longitudinal and mechanical.

43. Light slows down, bends toward the normal and has a shorter wavelength when it enters a medium with a higher index of refraction (n).

44. All angles in wave theory problems are measured to the normal.

45. Blue light has more energy, a shorter wavelength and a higher frequency than red light (remember- ROYGBIV).

46. The electromagnetic spectrum are listed highest energy (on left) to lowest (on right). They are all electromagnetic waves and travel at the speed of light (c = f *l ).

47. The speed (c) of all types of electromagnetic waves is 3.0 x 108 m/sec in a vacuum.

48. As the frequency of an electromagnetic wave increases its energy increases (E = h * f) and its wavelength decreases and its velocity remains constant as long as it doesn’t enter a medium with a different refractive index (i.e. optical density).

49. A prism produces a rainbow from white light by dispersion. (red bends the least because it slows the least).

50. Transverse wave particles vibrate back and forth perpendicular to the direction of the wave’s velocity. Longitudinal wave particles vibrate back and forth parallel to the direction of the wave’s velocity.

51. Light wave are transverse (they, and all (and only)transverse waves can be polarized).

52. The amplitude of a non-electromagnetic wave (i.e. water, string and sound waves) determines its energy. The frequency determines the pitch of a sound wave. Their wavelength is a function of its frequency and speed (v = f * l ). Their speed depends on the medium they are traveling in.

53. Constructive interference occurs when two waves are zero (0) degrees out of phase or a whole number of wavelengths (360 degrees.) out of phase.

54. At the critical angle a wave will be refracted to 90 degrees. At angles larger than the critical angle, light is reflected not refracted.

55. Doppler effect: when a wave source moves toward you, you will perceive waves with a shorter wavelength and higher frequency than the waves emitted by the source. When a wave source moves away from you, you will perceive waves with a longer wavelength and lower frequency.

56. Double slit diffraction works because of diffraction and interference.

57. Single slit diffraction produces a much wider central maximum than double slit.

58. Diffuse reflection occurs from dull surfaces while regular (spectacular) reflection occurs from smooth (mirror-like) surfaces.

59. Only waves show diffraction, interference and the polarization.

60. The period of a wave is the inverse of its frequency (T = 1/f ). So waves with higher frequencies have shorter periods.

61. Monochromatic light has one frequency.

62. Coherent light waves are all in phase.

V. Modern Physics

63. In order to explain the photoelectric effect, Einstein proposed particle behavior for light (and all electromagnetic waves) with E = h* f and KEmax = hf – Wo, where W is the work function.

64. A photon is a particle of light (wave packet).

65. To preserve the symmetry of the universe, DeBroglie proposed wave behavior for particles ( l = h/mv). Therefore large fast moving objects (baseballs, rockets) have very short wavelengths (that are unobservable) but very small objects, particularly when moving slowly have wavelengths that can be detected in the behavior of the objects.

66. Whenever charged particles are accelerated, electromagnetic waves are produced.

67. The lowest energy state of a atom is called the ground state.

68. Increasing light frequency increases the kinetic energy of the emitted photo-electrons in the photo-electric effect (KEmax = hf – Wo).

69. As the threshold frequency increases for a photo-cell (photo emissive material) the work function also increases (Wo = h fo)

70. Increasing light intensity increases the number of emitted photo-electrons in the photo-electric effect but not their KE (i.e. more intensity>more photons>more electrons emitted). This is the particle nature shown by light.

VI. Motion in a plane

71. Key to understanding trajectories is to separate the motion into two independent components in different dimensions – normally horizontal and vertical. Usually the velocity in the horizontal dimension is constant (not accelerated) and the motion in the vertical dimension is changing (usually with acceleration of g).

72. Centripetal force and centripetal acceleration vectors are toward the center of the circle- while the velocity vector is tangent to the circle. (Centripetal means towards the center!)

73. An object in orbit is not weightless – it is its weight that keeps it moving in a circle around the astronomical mass it is orbiting. In other words, its weight is the centripetal force keeping it moving in a circle.

74. An object in orbit is in free fall – it is falling freely in response to its own weight. Any object inside a freely falling object will appear to be weightless.

75. Rutherford discovered the positive nucleus using his famous gold-foil experiment.

76. Fusion is the process in which hydrogen is combined to make helium.

77. Fission requires that a neutron causes uranium to be split into middle size atoms and produce extra neutrons, which, in turn, can go on and cause more fissions.

78. Radioactive half-lives are not effected by any changes in temperature or pressure (or anything else for that matter).

79. One AMU of mass is equal to 931 MeV of energy. (E = mc2). This is on the Reference Charts!

80. Nuclear forces are very strong and very short-ranged.

81. There are two basic types of elementary particles: Hadrons & Leptons (see Chart).

82. There are two types of Hadrons: Baryons and Mesons (see Chart).

83. The two types of Hadrons are different because they are made up of different numbers of quarks. Baryons are made up of 3 quarks, and Mesons of a quark and antiquark.

84. Notice that to make long-lived Hadron particles quarks must combine in such a way as to give the charge of particle formed a multiple of the elementary charge.

85. For every particle in the "Standard Model" there is an antiparticle. The major difference of an antipartcle is that its charge is opposite in sign. All antiparticles will anhililate as soon as they come in contact with matter and will release a great amount of energy.

85. Notice that to make long-lived Hadron particles quarks must combine in such a way as to give the charge of particle formed a multiple of the elementary charge.

86. Notice that the retention of the Energy Level Diagrams on the new charts implies that there will be questions on it. The units (eV) can be converted to Joules with the coversion given on the first Chart of the Regents Reference tables. And can be used with the formula (given under Modern Physics formulas) to calculate the energy absorbed or released when the electron changes levels.

And by using another formula (given under Modern Physics formulas) you can calculate the frequency of electromagnetic radiation absorbed or released. AND using the Electro-magnetic spectrom given on the charts you can find out what kind of electromagnetic radiation it is (infrared, visible light, UV light, etc.)

87. Physics is phun!! (This is key. Honest!)

The Standard Model of Particle Physics

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The current model of sub-atomic structure used to understand matter is known as the Standard Model.  Development of this model began in the late 1960s, and has continued through today with contributions from many scientists across the world.  The Standard Model explains the interactions of the strong (nuclear), electromagnetic, and weak forces, but has yet to account for the gravitational force.  The search for the theorized Higgs Boson at Fermilab and CERN is an attempt to better unify and strengthen the Standard Model.

Although the Standard Model itself is a very complicated theory, the basic structure of the model is fairly straightforward.  According to the model, all matter is divided into two categories, known as hadrons and the much smaller leptons.  All of the fundamental forces act on hadrons, which include
particles such as protons and neutrons.  In contrast, the strong nuclear force doesn’t act on leptons, so only three fundamental forces act on leptons such as electrons, positrons, muons, tau particles and neutrinos.

Hadrons are further divided into baryons and mesons.  Baryons such as protons and neutrons are composed of three smaller particles known as quarks.  Charges of baryons are always whole numbers.  Mesons are composed of a quark and an anti-quark (for example, an up quark and an antidown
quark).  If this sounds like a lot to keep track of, have no fear, this is summarized for you on the Regents Physics Reference Table.

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Scientists have identified six types of quarks.  For each of the six types of quarks, there also exists a corresponding anti-quark with an opposite charge.  The quarks have rather interesting names: up quark, down quark, charm quark, strange quark, top quark, and bottom quark.  Charges on each quark are either one third of an elementary charge, or two thirds of an elementary charge, positive or negative, and the quarks are symbolized by the first letter of their name.  For the associated anti-quark, the symbol is the first letter of the anti-quark’s name, with a line over the name.  For example, the symbol for the up quark is u.  The symbol for the anti-up quark is ū.

Similarly, scientists have identified six types of leptons: the electron, the muon, the tau particle, and the electron neutrino, muon neutrino, and tau neutrino.  Again, for each of these leptons there also exists an associated anti-lepton. The most familiar lepton, the electron, has a charge of -1e.  Its anti-particle, the positron, has a charge of +1e.

Mass-Energy Equivalence

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Mass and energy are two concepts effectively describing the same thing, therefore we could more appropriately combine these two laws into a single law: the law of conservation of mass-energy.  This law states that mass-energy cannot be created nor destroyed.

The universal conservation laws we have studied so far this course include:

  • Conservation of Mass-Energy
  • Conservation of Chargesmart_guy_with_emc2_hg_clr
  • Conservation of Momentum

 
Einstein’s famous formula, E=mc^2, relates the amount of energy contained in matter to the mass times the speed of light in a vacuum (c=3×10^8 m/s) squared.  Theoretically, then, we could determine the amount of energy represented by 1 kilogram of matter as follows:

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More practically, however, it is not realistic to convert large quantities of mass completely into energy.  Current practice revolves around converting small amounts of mass into energy in nuclear processes.

Typically these masses are so small that measuring in units of kilograms is cumbersome.  Instead, scientists often work with the much smaller universal mass unit (u), which is equal in mass to one-twelfth the mass of a single atom of Carbon-12.  The mass of a proton and neutron, therefore, is close to 1u, and the mass of an electron is close to 5×10-4u.  In precise terms, 1u=1.66053886×10-27kg.

One universal mass unit (1u) completely converted to energy is equivalent to 931 MeV.  Because mass and energy are different forms of the same thing, this could even be considered a unit conversion problem.  If given a mass in universal mass units, you can use this equivalence directly from the front of the Regents Physics Reference Table to solve for the equivalent amount of energy, without having to convert into standard units and utilize the E=mc^2 equation.

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Emission and Absorption Spectra

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Once you understand the energy level diagram, it quickly becomes obvious that atoms can only emit certain frequencies of photons, correlating to the difference between energy levels as an electron falls from a higher energy state to a lower energy state.  In similar fashion, electrons can only absorb
photons with energy equal to the difference in energy levels as the electron jumps from a lower to a higher energy state.  This leads to unique atomic spectra of emitted radiation for each element.

 

An object that is heated to the point where it glows (incandescence) emits a continuous energy spectrum, described as  blackbody radiation.

If a gas-discharge lamp is made from mercury vapor, the mercury vapor is made to emit light by application of a high electrical potential.  The light emitted by the mercury vapor is created by electrons in higher energy states falling to lower energy states, therefore the photons emitted correspond directly in wavelength to the difference in energy levels of the electrons.  This creates a unique spectrum of frequencies which can be observed by separating the colors using a prism, known as an  emission spectrum.  By analyzing the emission spectra of various objects, scientists can determine the composition of those objects.

In similar fashion, if light of all colors is shone through a cold gas, the gas will only absorb the frequencies corresponding to photon energies exactly equal to the difference between the gas’s atomic energy levels.  This creates a spectrum with all colors except those absorbed by the gas, known as an  absorption spectrum.

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