**Regents Physics Exam Prep: 101 Facts You Should Know**

Compiled by Jim Davidson, High School Physics Teacher

Compiled by Jim Davidson, High School Physics Teacher

- Weight (force of gravity) decreases as you move away from the earth by distance squared.
- Mass and inertia are the same thing.
- 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-tine 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** - 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** - 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** - 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** - 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 10
^{8}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 .
- The atomic number is equal to the number of protons (2 for alpha)
- Deuterium () is an isotope of hydrogen ()
- 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 (), beta () 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.
**General** - The most important formulas in the physics regents are:
- Physics is fun. (Honest!)

**Mechanics**

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