Transcript Photon Energy

Physics Regents Review
2011
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.k12.ny.us/
GNPS/SHS/dept/science/wells/re
gentswkbk.pdf
Know Scalars and
Vectors
• SCALARS
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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=0m/s
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 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
• 9.81m/s2 at the
surface of the earth
• it is a uniform field
• neglect air
resistance
Gravity Goes......???
• 9.8m/s2
• 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/s2
• 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/ra
refaction
• 1Hz 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
• 1ampere 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
• 1W=1V/1A
• 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
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
of quantized
light
• the ‘reverse
light bulb’
• Proof that light
is a particle
• contributes to
photon collision
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
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