Modern Physics Photon Energy Scalar photon bundle of
Modern Physics
Photon Energy • Scalar • photon - bundle of light • use Planck’s constant • directly related to frequency • inversely related to wavelength
Photoelectric Effect • Einstein’s demo • Proof that light of quantized is a particle light • contributes to • the ‘reverse light photon collision bulb’ theory
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 Me. V
Universal Mass Units • Don’t use E=mc 2 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 n 0 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 AND METHODS
Math Resources – Bring pens, pencils, calculator, protractor
PRACTICE • http: //www. greatneck. k 12. ny. us/ GNPS/SHS/dept/science/wells/re gentswkbk. pdf
Know Scalars and Vectors • SCALARS • Speed • Distance • Mass • Time • Energy • Power • VECTORS • Velocity • Displacement • Acceleration • Force (and weight) • Momentum • Field
What is the distance? What is the displacement?
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
Identify the variables in each problem statement
At rest means v=0 m/s
Acceleration • Acceleration is always a vector • slope of velocity v. time graph • 9. 81 m/s 2 for freefall
The only acceleration of a projectile is 9. 8 m/s 2 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. 81 m/s 2 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 speed Slope 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
Time connects vertical motion to horizontal motion
What is Force?
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 PLANE Force parallel is Wsinq Force 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
Universal gravitation is an inverse square relationship
The sun is one focus of the solar system ellipse Satellite speed is fastest closer to the body it travels around Geosynchronous orbit period is 1 day ORBITS!
Gravitaional Field • vector. . . newtons • the accelerational field is the same as acc. due to gravity • 9. 81 m/s 2 at the surface of the earth • it is a uniform field • neglect air resistance
Gravity Goes. . . ? ? ? • 9. 8 m/s 2 • neglect air resistance
DOWN!!!!!!
Weight always acts down
Momentum • Vector. . . kg*m/s • mass times speed • increases with inertia
Energy and momentum are conserved in elastic collisions
CRASH!
EXPLOSIONS!
Conservation of Momentum • momentum is always conserved • explosions pbefore is zero • in elastic collisions, energy is conserved
Impulse/ Change in Momentum • vector. . kg*m/s • every collision has an impulse • each object gets the same force for the same time • the less massive object accelerates
Spring Force - Hookes Law • Vector. . newton s • the force is proportional to the stretch • each spring has a different spring constant, k • units for k. . N/m
WOW – Springs are so cool!
X – the change in length of the spring!!!
Spring Energy-energy of position • Scalar. . joules • direct square with stretch • need the spring constant
How much energy? ? ?
Centripetal Force • Vector. . newtons • directed toward the center • can be the result of other forces
That spinning lab
Centripetal Acceleration • Vector. . m/s 2 • directed toward the center of the circle • speed is always tangent to the circle
It is directed to the center
Potential Energy • Scalar. . . joules • stored energy • increases as height increases
Falling on a roller coaster
Kinetic Energy • Scalar. . joules • energy of motion • direct square with speed
Speed is kinetic
Work • Scalar. . joules • force and distance must be colinear • interrelated with energy
Work can be done against gravity
No movement … means no work
Pendulums conserve Energy
And spring catapults too
Total Energy • Scalar. . joules • all PE can become KE if an object falls/slides with no friction • includes mechanical energy and heat
Energy and Work are interchangeable
Power. . . the rate of Work • Scalar. . watts • it is the rate of work
Less time per work means higher power
WAVES
Period of a Wave (or repetitive motion) • Scalar • it is the time for one complete cycle • crest/trough. . . or. . . compression/r arefaction • 1 Hz is 1/s
Wave Speed equation • Scalar • wave propagation is through a medium for mechanical waves • electromagnetic waves need no medium
Wave Properties • All waves have: • amplitude (height) • frequency (rate) • wavelength (distance) • speed ( based on medium) • • amplitude. . meters frequency. . hertz wavelength. . . meters speed. . . m/s
Equations That Relate to Acoustic Guitars • V= f • T=1/f • V=d/t
Physics terms related to Guitar • Tone- is a single frequency tone with no harmonic content • Pitch-the perceived frequency of a note or sound • Wavelength- Length of the wave (duh) • Node- a point on a wave that remains still • Frequency- is a measure of the number of occurrences of a repeating event per unit time.
Electromagnetic Spectrum • ‘Light’ means all Emag • every electric field has a corresponding perpendicular magnetic field • wave types can overlap
Law of Reflection • angles with respect to the normal • included angle is double each angle • parallel light reflects parallel for regular ref. • reflected rays cross in diffuse ref.
Index of Refraction of Light • indexed in comparision to a vacuum (or air) • high index is slow speed • light includes all Emag radiation • c = 3. 00 x 108 m/s
Index of Refraction • every translucent material has a speed for light • air is fastest • diamond is slowest
Snell’s Law for Refraction • rays bend as the pass a boundary • FAST • Fast to Slow Toward • Slow to Fast Away • all angles with respect to the normal
Refraction Lab
Changes across a Boundary • higher index has slower speed • higher index has shorter wavelength • frequency is constant
Bridge
Bridge with resonance
Bridge with resonance breaking
Bridge with large amplitude resonance
Electrostatic Force • vector. . newton s • much like gravitational field • direct with charge (q) in coulombs • inverse square with distance (r)
Problem • 62 On the axes in your answer booklet, sketch a graph showing the relationship between the magnitude of the electrostatic force between the two charged particles and the distance between the centers of the particles. [1]
Electric field • vector. . . N/C • much like gravity field • direction always based on the direction a positive would move • opposites attract • like charges repel
E – fields are all around us
Electric Potential • scalar. . . volt. . (J/ C) • there is no gravity corollary • can be called voltage, voltage drop, potential difference, or potential drop
Potential Difference is Voltage
Lighting is charge jumping across potential difference - current
Current • scalar. . ampere • 1 ampere is one coulomb per second • current is a rate of electron flow • must know the charge on an electron (or proton)
Current is like water flowing
Resistance. . Ohm’s Law • scalar. . ohm • 1 W=1 V/1 A • heaters are linear resistors. . . this equation fits • lamps are not linear resistors
Resistors are like narrow doorways for current
Resistance of metals (wires) • scalar. . . ohms • increases with increased length • decreases with increased crosssectional area • look up the material on the table
Short fat cold wires have low resistance
Resistivity • use only to determine the material resistance of a wire • high values have more resistance • be careful with exponents
Electric Power • Scalar. . watt • look for the word ‘rate” • can relate to mechanics • conserved in transformers
Power always adds up
Electric Energy • Scalar. . joules • look for the word “amount” • can relate to mechanics • multiply by decimal for percentage of efficiency
draw circuits • a circuit must be a closed loop • series. . one path • parallel. . . multipl e paths • add voltmeters ‘across’ • add ammeters ‘in line’
Series Circuits • Current is the same through each resistor • Voltages add up to the total from source • Resistors add up • each added resistor increases the
Parallel Circuits • Currents from each path add up to total • Voltage (push) is the same across each resistor • Resitors add as reciprocals • each added resistor decreases the total
- Slides: 129