♛ Mechanics
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► Weight (force of gravity) decreases as you move away from the earth by distance squared.
► Constant velocity and zero velocity means the net force is zero and acceleration is zero.
► Weight (in newtons) is mass x acceleration (w = mg). Mass is not weight!
► Velocity, displacement [s], momentum, force and acceleration are vectors.
► Speed, distance [d], time, and energy (joules) are scalar quantities.
► The slope of the velocity-time graph is acceleration.
► 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 difference to the sum is the total range of possible resultants.
► Centripetal force and centripetal acceleration vectors are toward the center of the circle- while the velocity vector is tangent to the circle.
► An unbalanced force (object not in equilibrium) must produce acceleration.
► The slope of the distance-time graph is velocity.
► The equilibrant force is equal in magnitude but opposite in direction to the resultant vector.
► Momentum is conserved in all collision systems.
► Magnitude is a term use to state how large a vector quantity is.
♛ Energy
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► Mechanical energy is the sum of the potential and kinetic energy.
Units:
a = [m/sec^2],
F = [kg*m/sec^2] (newton),
work = Pe= Ke = [kg*m^2/sec^2] (joule)
► An Ev is an energy unit equal to 1.6 x 10-19 joules
► Gravitational potential energy increases as height increases.
► Kinetic energy changes only if velocity changes.
► Mechanical energy (Pe + Ke) does not change for a free falling mass or a swinging pendulum. (when ignoring air friction)
► The units for power are [joules/sec] or the rate of change of energy.
♛ Electricity
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► A coulomb is charge, an amp is current [coulomb/sec] and a volt is potential difference [joule/coulomb].
► Short fat cold wires make the best conductors.
► Electrons and protons have equal amounts of charge (1.6 x 10-19 coulombs each).
► Adding a resistor in parallel decreases the total resistance of a circuit.
► Adding a resistor in series increases the total resistance of a circuit.
► All resistors in series have equal current (I).
► All resistors in parallel have equal voltage (V).
► If two charged spheres touch each other add the charges and divide by two to find the final charge on each sphere.
► Insulators contain no free electrons.
► Ionized gases conduct electric current using positive ions, negative ions and electrons.
► Electric fields all point in the direction of the force on a positive test charge.
► Electric fields between two parallel plates are uniform in strength except at the edges.
► Millikan determined the charge on a single electron using his famous oil-drop experiment.
► All charge changes result from the movement of electrons not protons (an object becomes positive by losing electrons)
♛ Magnetism
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► The direction of a magnetic field is defined by the direction a compass needle points.
► Magnetic fields point from the north to the south outside the magnet and south to north inside the magnet.
► Magnetic flux is measured in webers.
► Left hands are for negative charges and right hands are for positive charges.
► The first hand rule deals with the B-field around a current bearing wire, the third hand rule looks at the force on charges moving in a
► B-field, and the second hand rule is redundant.
► Solenoids are stronger with more current or more wire turns or adding a soft iron core.
♛ Wave Phenomena
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► Sound waves are longitudinal and mechanical.
► Light slows down, bends toward the normal and has a shorter wavelength when it enters a higher (n) value medium.
► All angles in wave theory problems are measured to the normal.
► Blue light has more energy. A shorter wavelength and a higher frequency than red light (remember- ROYGBIV).
► The electromagnetic spectrum (radio, infrared, visible. Ultraviolet x-ray and gamma) are listed lowest energy to highest.
► A prism produces a rainbow from white light by dispersion (red bends the least because it slows the least).
► Light wave are transverse (they can be polarized).
► The speed of all types of electromagnetic waves is 3.0 x 108 m/sec in a vacuum.
► The amplitude of a sound wave determines its energy.
► Constructive interference occurs when two waves are zero (0) degrees out of phase or a whole number of wavelengths (360 degrees.) out of phase.
► At the critical angle a wave will be refracted to 90 degrees.
► According to the Doppler effect a wave source moving toward you will generate waves with a shorter wavelength and higher frequency.
► Double slit diffraction works because of diffraction and interference.
► Single slit diffraction produces a much wider central maximum than double slit.
► Diffuse reflection occurs from dull surfaces while regular reflection occurs from mirror type surfaces.
► As the frequency of a wave increases its energy increases and its wavelength decreases.
► Transverse wave particles vibrate back and forth perpendicular to the wave direction.
► Wave behavior is proven by diffraction, interference and the polarization of light.
► Shorter waves with higher frequencies have shorter periods.
► Radiowaves are electromagnetic and travel at the speed of light (c).
► Monochromatic light has one frequency.
► Coherent light waves are all in phase.
♛ Geometric Optics
-------------------------
► Real images are always inverted.
► Virtual images are always upright.
► Diverging lens (concave) produce only small virtual images.
► Light rays bend away from the normal as they gain speed and a longer wavelength by entering a slower (n) medium {frequency remains constant}.
► The focal length of a converging lens (convex) is shorter with a higher (n) value lens or if blue light replaces red.
♛ Modern Physics
-----------------------
► The particle behavior of light is proven by the photoelectric effect.
► A photon is a particle of light {wave packet}.
► Large objects have very short wavelengths when moving and thus can not be observed behaving as a wave. (DeBroglie Waves)
► All electromagnetic waves originate from accelerating charged particles.
► The frequency of a light wave determines its energy (E = hf).
► The lowest energy state of a atom is called the ground state.
► Increasing light frequency increases the kinetic energy of the emitted photo-electrons.
► As the threshold frequency increase for a photo-cell (photo emissive material) the work function also increases.
► Increasing light intensity increases the number of emitted photo-electrons but not their KE.
♛ Internal Energy
----------------------
► Internal energy is the sum of temperature (ke) and phase (pe) conditions.
► Steam and liquid water molecules at 100 degrees have equal kinetic energies.
► Degrees Kelvin (absolute temp.) Is equal to zero (0) degrees Celsius.
► Temperature measures the average kinetic energy of the molecules.
► Phase changes are due to potential energy changes.
► Internal energy always flows from an object at higher temperature to one of lower temperature.
♛ Nuclear Physics
----------------------
► Alpha particles are the same as helium nuclei and have the symbol 4He2.
► The atomic number is equal to the number of protons (2 for alpha)
► Deuterium (2H1) is an isotope of hydrogen (1H1)
► The number of nucleons is equal to protons + neutrons (4 for alpha)
► Only charged particles can be accelerated in a particle accelerator such as a cyclotron or Van Der Graaf generator.
► Natural radiation is alpha (4He2), beta (0e-1) and gamma (high energy x-rays)
► A loss of a beta particle results in an increase in atomic number.
► All nuclei weigh less than their parts. This mass defect is converted into binding energy. (E=mc^2)
► Isotopes have different neutron numbers and atomic masses but the same number of protons (atomic numbers).
► Geiger counters, photographic plates, cloud and bubble chambers are all used to detect or observe radiation.
► Rutherford discovered the positive nucleus using his famous gold-foil experiment.
► Fusion requires that hydrogen be combined to make helium.
► Fission requires that a neutron causes uranium to be split into middle size atoms and produce extra neutrons.
► Radioactive half-lives can not be changed by heat or pressure.
► One AMU of mass is equal to 931 meV of energy (E = mc^2).
► Nuclear forces are strong and short ranged.
Courtesy : http://regentsprep.org/regents/physics/101facts/101facts.cfm
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