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## Modern Physics

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**Photon Energy**• Scalar • photon - bundle of light • use Planck’s constant • directly related to frequency • inversely related to wavelength**Einstein’s demo of quantized light**the ‘reverse light bulb’ Proof that light is a particle contributes to photon collision theory Photoelectric Effect**Bohr Model**• electrons fit in exact energy levels • quantized energy • release photon as electron falls • absorb photon (or other energy) as electron jumps up**Hydrogen Energy Levels**• know the Balmer series is visible • use energy difference to know posible jumps • same for mercury energy levels**Energy equivalent of mass**• mass can change to energy • use c= 3.00 x 108 m/s • kg relates to J • amu relates to MeV**Universal Mass Units**• Don’t use E=mc2 for universal mass units • Just use the conversion factor given**Classification of Matter**• there are subparticle beyond the protons and neutrons...but they don’t stand alone • p+ and n0 are baryons • e- are leptons • the sum of quarks is always an integer**Particles of the Standard Model**• the first column defines protons neutrons and electrons • antiparticles have a bar above the symbol • antiparticles have opposite magnetic moment and charge**Physics Regents Review 2009**Welcome to the Physics Regents Exams St. Mary's Physics Online**Math Resources – Bring pens, pencils, calculator,**protractor**PRACTICE**• http://www.greatneck.k12.ny.us/GNPS/SHS/dept/science/wells/regentswkbk.pdf**Know Scalars and Vectors**• SCALARS • Speed • Distance • Mass • Time • Energy • Power • VECTORS • Velocity • Displacement • Acceleration • Force (and weight) • Momentum • Field**Resultant of any two vectors fall between max at (sum) and**min (difference)**Speed and Velocity**• speed - scalar • velocity - vector • this is the slope of the distance v. time graph • memorize that average can also be final plus initial divided by two**Acceleration**• Acceleration is always a vector • slope of velocity v. time graph • 9.81m/s2 for freefall**The only acceleration of a projectile is 9.8m/s2 vertically**down**Final Speed**• same as acceleration equation • we only calculate constant uniform acceleration problems**The distance equation**• most common equation for freefall and projectiles • Vi is zero for freefall • a is 9.81m/s2 for y direction near the earth**The no time motion equation!**• use when time is not given • usually Vi or Vf is zero**Mass v Weight**• Inertia is mass • Weight always acts down • Mass does not depend upon position, weight does**Slope of displacement v. time is speedSlope of speed v. time**is acceleration**Resolving vectors into components**projectile speed V can become Vx and Vy Force at an angle can become Fx and Fy**F=ma....Newton’s Second Law**• The most important equation in mechanics! • Fnet is the sum of all the forces ... • this equation can be applied in any one dimension**Frictional Force**• Vector • Normal force is weight if on a horizontal surface • Always opposes motion or intended motion • does not depend on surface area**Friction does not conserve mechanical energy- it transforms**energy to heat**Friction opposes relative motion between the objects in**contact (opposes the direction of velocity)**INCLINED PLANEForce parallel is WsinqForce perpendicular is**Wcosq**Problem**• A 1200-kilogram car moving at 12 meters per second collides with a 2300-kilogram car • that is waiting at rest at a traffic light. After the collision, the cars lock together and slide. • Eventually, the combined cars are brought to rest by a force of kinetic friction as the • rubber tires slide across the dry, level, asphalt road surface. • 59 Calculate the speed of the locked-together cars immediately after the collision. [Show all work, including • the equation and substitution with units.] [2]**Coefficient of Friction**• no units • depends on the materials in contact • unaffected by area • kinetic is moving • static is resisting motion**Universal Gravitation**• Vector ....newtons • depends on each mass • decreases as distance (r) increases**The sun is one focus of the solar system ellipse Satellite**speed is fastest closer to the body it travels aroundGeosynchronous orbit period is 1 day ORBITS!**Gravitaional Field**• vector...newtons • the accelerational field is the same as acc. due to gravity • 9.81m/s2 at the surface of the earth • it is a uniform field • neglect air resistance**Gravity Goes......???**• 9.8m/s2 • neglect air resistance