Physics Flashcards
Direction of electric field lines
direction a positive charge would move in presence of source charge
- negative source charge- toward it (radiate towards)
- positive source charge- radiate away
Force vector vs electric field vectors
Positive charge- force vector in same direction as field lines
Negative charge- force vector opposite direction as field lines
Recite equations for Fe, E, V, U
Lols not writing this shit
Signs of V
positive for +, negative for -, scalar
Potential difference
Wab/q- conservative force is Wab.
Positive charge- delta V=negative, Wab negative
Negative charge= delta V-positive, Wab negative. Electric potential energy decreases.
External E field affect on dipole
Net torque- forces cancel tho- align with E
torque= pEsin(theta)
Magnetic field- what causes + units
Tesla (big), Gauss (small) - generated by moving charge
Diamagnetic
no unpaired electrons- no net magnetic field-wood, glass, etc.
Paramagnetic
unpaired electrons-net magnetic dipole moment but no magnetic field- weakly magnetized in presence of external field- copper, aluminum
Ferromagnetic
no net magnetic dipole, unpaired e-…. will be strongly magnetized in response to field/temps
iron, nickel, cobalt
Equation for straight current carrying wire, B
right hand rule please- thumb in direction of current, fingers curl around wire B- and im not writing this shit look it up
equation for circular loop of wire, radius r, magnetic field in center
just remove the pi on the bottom
Magnetic force- moving charge
qvBsin(theta) theta between v and B. Thumb v, B- pointer, middle- force
Magnetic force-current carrying wire
ILBsin(theta)- thumb current, B- pointer, middle-force
Direction of current
direction of + charge flow, amount of charge flowing per time
Kirchhoff rules
current into=current out of junction,
sum of voltage sources= sum of voltage drops
Resistance equation
pL/A
increases with length, decreases with area
high temp- usually higher R
Ohm’s Law
V=IR
Power in circuit formula- must memorize
P=IV, I^2R, V^2/R
rint
V=emf-rinternal. Mcat, batteries ideal
Resistors in series
add up resistances, add up voltages. resistence increases with more resistors, current same for all
Resistors in parallel
voltage same for all pathways, current splits- more current where less resistance, lower equivalent resistors, add inverses!
Ammeter vs voltmeter
Ammeter- in series, low resistance
Voltmeter- in parallel
Ommeter
no circuit needed
capacitance formula
C=Q/V, units= farads
C=A/d* permittivity
Electric field between capacitor plates
Uniform field E=V/d (positive to negative direction)
Potential energy of capacitor
U=0.5CV^2
Dielectric material
When put in between capacitor plates- increases capacitance by dielectric constant
C’=kC
Isolated capacitor - dielectric
voltage decreases, C up
Capacitor in circuit- dielectric insert
Q increases, V same, C increases
Capacitors in series
equivalent capacitance decreases - like parallel resistors. Add inverse. Voltage= sum of voltages
Capacitors in parallel
equivalent capacitance increases- add normally - like series resistors. Voltage= same for all
Photoelectric effect
light of high frequency hits metal in vacumn- emitting electrons.
Photoelectric effect
Current ?
light of high frequency hits metal in vacuum- emitting electrons.
ejected electrons create current, proportional to intensity of incident light beam
Energy of photons
E=hf. H=6.626E-34 Js
Max kinetic energy of photon
Kmax= hf-W, W=h*threshold frequency W= minimum energy required to eject electron
Fluorescence- how?
Species absorbs high frequency light and returns to its ground state in multiple steps. Each step has less energy absorbed light and is within visible light of spectrum
Mass defect
Difference between mass of unbounded nucleons and mass of bounded nucleons- energy released by bounded nucleons.
Unbounded- more energy+ more mass. Mass defect is amount of mass converted to energy in nuclear fission
Mass of nucleus is slightly lower than mass of protons+nuetrons. Defect in mass is result of mass that has been converted to energy- E=mc^2.
Mass defect
Difference between mass of unbounded nucleons and mass of bounded nucleons- energy released by bounded nucleons.
Unbounded- more energy+ more mass.
Mass defect is amount of mass converted to energy in nuclear fission
Mass of nucleus is slightly lower than mass of protons+nuetrons. Defect in mass is result of mass that has been converted to energy- E=mc^2.
Binding energy
Energy released when nucleons (protons and nuetrons) bind together in nucleus. More binding energy per nucleon released, more stable the nucleus
Weak nuclear force
stability of nucleus- slightly contribute
Nuclear fusion
small nuclei combine to form larger nucleus
how stars power themselves- fuse hydrogen nuclei to make helium nuclei
Nuclear fusion
large nucleus splits into smaller nuclei
fission rxns that release more neutrons will cause nearby atoms to undergo fission also
nuclear power plants
Radioactive decay definition
spontaneous decay of certain nuclei accompanied by emission of specific particle
Alpha decay
emission of alpha particle- helium nucleus—- two protons, two neutrons, no electrons
2- atomic number, 4- mass +
beta- decay
neutron is converted to a proton
1+ atomic number, 0 change in mass #
beta particle emitted- electron
beta+ decay
proton converted to neutron
1- atomic number, 0 change in mass #
positron emitted
Gamma decay
emission of gamma rays, no change in mass or atomic number
Electron capture
add electron so same mass number, 1- atomic number
Equation of exponential decay
n=n0 e^(-λt)
decay constant relationship to half life
λ=ln2/Thalf
decay constant relationship to half life
λ=ln2/Thalf
Transversal waves
direction of particle oscillation is perpendicular to propagation of wave - electromagnetic waves
Longitudinal waves
direction of particle oscillation is parallel to propagation of wave- sound waves
Wave equations
v=fλ, T=1/f, w=2pif
Constructive interferance
waves in phase- amplitudes add
Destructive interferance
waves out of phase- amplitudes cancel out
Traveling wave
if reflected, incident and reflected wave are interfering with eachother (only one end fixed of string and other end open)
Standing waves
String with both ends fixed/pipe with both ends or one end open
waves in opposite directions interfere with eachother
traveling wave and reflected wave appears to be stationary- fluctuation of amplitude at fixed points on string- no displacement of points on ot
node- rest
antinodes- max amplitude
closed boundaries- no oscillation- nodes
open boundaries- maximal oscillation- antinodes
Timbre
quality of sound caused by vibration- determined by the natural- resonant- frequency of object.
Hearing frequency range audible
20 Hz to 20000 Hz- high frequency hearing declines with age
Damping/attenuation
Decrease in amplitude caused by applied/nonconservative force, such as friction, air resistance, viscous drag
for sound, amplitude, intensity, and sound level all decrease
no effect on frequency/pitch
negligible on test unless specified
Forced oscillation
Periodically varying force applied to waves. If frequency of applied force is similar to natural frequency- amplitude grows
Resonating system
force frequency=natural frequency- amplitude of oscillation is at a max and if frictionless, amplitude increase indefinitely - energy of system increase
Sound
longitudinal wave- transmitted by oscillation/mechanical vibration of particles in deformable medium
Speed of sound, formula, and of air
v=sqrt(B/p)
B= measure of medium resistance to compression, solids have highest
p= density
air= 343 m/s at 20 degrees C
Production of sound- human body
As air moves past vocal cords, they vibrate and make air vibrate at same frequency. Pitch=frequency and is controlled by varying tension of cords
Infrasonic waves
sound waves with frequencies <20 Hz
Ultrasonic waves
sound waves with frequencies >20000 Hz
Doppler effect
difference between actual frequency of sound and its percieved frequency f’ when source of sound and sounds detector are moving relative to one another
if moving toward eachother- f’ > f- percieve higher
if moving away from eachother- f’
Dopper effect equation logistics
in front of moving object= compressed (high freqency)
behind moving object= stretched waves (lower frequency)
not writing equation too much work.
Numerator deals with sound detector
Denominator deals with sound source
For both- if moving towards other thing= pick top sign. If moving away from other thing= pick bottom sign
Shock waves
Object producing sound while traveling at or above the speed of sound
Waves build upon eachother- higher amplitude- high pressures!
High pressure followed by low pressure= sonic boon
Sound intensity
average rate of energy transfer per area across surface perpendicular to wave—
power/area
I=P/A
I=kA^2 (proportional to square of amplitude)
I=k/d^2 (inversely proportional to square of distance- more distance= more area)
perceived as volume/loudness
Sound level (beta)
Measured in decibels dB
Logarithmic scale
I=intensity
I0= threshold of hearing 1E-12 W/m^2
B= 10log(I/I0)
If intensity of sound changed
Bt=Bi+10log(It/Ti)
It= final intensity, Ti= initial intensity
beat frequency
when two slightly different frequencies produced in proximity leads to volume varying periodically.
Fbeat= frequency of volume variation
fbeat=absolute value (f1-f2)
f1/f2= two frequencies
ultrasound
machine consists of transmitter to generate pressure gradient and also a receiver to process reflected sound
speed, travel time known= can create graphical representation based on distances
ultrasound-high frequency
Doppler ultrasound
determine flow of blood- detect frequency shift associated with movement toward/away from reciever
Standing waves section
YOU NEED TO FINISH
Therapeutic effects of ultrasound
- increase blood flow to a site of injury in deep tissue to promote healing since create friction and heat
- focusing a sound wave=high energy specific point to break up kidney stones and destroy tumors
- dental cleaning
- destruction of cataracts
string standing wave formulas for frequency and wavelength
wavelength: λ=2L/n (n=harmonic- starts at 1 for only one antinode)
number of antinodes= hills= harmonic number
f=nv/2L
fundamental frequency
1st harmonic frequency- lowest frequency possible in the string standing wave. All possible frequencies=harmonic series
open pipe standing wave
open ends= antinodes
wavelength= 2L/n
f=nv/2L
number of nodes= harmonic number
closed pipe standing wave
1st harmonic= one node at closed end, antinode at open end
λ=4L/n
f=nv/4L
harmonics can only be odd integers
harmonics given by number of quarter wavelengths in pipe
Gravitation equation
Fg=Gmm/r^2
Center of mass
weighted average of masses at each location
Kinematics equations
v=vo+at
x=vot + at^2/2
v^2= (vo)^2+ 2ax
x=vt no acceleration
Centripetal force
Fc= mv^2/r
torque
r xF= rFsin(theta)
Components of gravity on inclined plane
mgsin(theta)- parallel
mgcos(theta)- perpendicular
Static friction vs kinetic friction
kinetic=sliding, constant value
static friction=stationary, varying values dependent on magnitude of applied force, and icnreases with SA of object
coefficient of static friction always greater than coefficient of kinetic friction
F=mu* N
Work
change in energy= Fdcos(theta)= P* delta V
in isovolumetric/isochoric processes, W=0 since delta V=0
power
W/t
work energy theorem
net work= change in kinetic energy
C to F
9/5C+32
thermal expansion
delta L= alpha* L * delta T
alpha= coefficient of linear expansion
solids expand in length
first law of thermo
Delta U= Q-W (heat flow in- work done by system)= internal energy change
volume expansion
delta V= beta* V* delta T
beta= coefficient of volumetric expansion
liquids expand in volume
second law of thermo
entropy of universe is always positive
heat change
q=mc delta T
q= mL (L= heat of transformation )- phase change, T constant
Simple machines
Provide mechanical advantage- inclined plane, wedge(like pick axe), wheel and axle, pulley, screw
Mechanical advantage
Fout/Fin
Fout= force exerted on object by machine Fin= force actually applied to machine
using simple machines mean less force can be applied to create lots of force
reduced force applied, but must be applied over longer distance to keep work the same
Pulley mechanical advantage
to pull object certain height in air (load distance), one mustpull through a length of rope (effort distance) equal o twice that displacement
Efficiency
Wout/Win=
load* load distance)/(effort* effort distance
speed of light equation
frequency*wavelength =c
c=3E8 m/s
