physics 2 Flashcards
What is static vs dynamic equilibrium?
static- objects at rest
dynamic - objects moving at constant velocity
both - net force experienced by object is zero
If an object is “stationary” or exactly “balanced”, they are in ___
equilibrium
What is the formula for Torque? Torque for gravity?
T= Fl or T= Frsin(theta)
gravity - T= mgl
F - force
l - lever arm
r- distance between the force and point of rotation
In what specific situations should you use T= Frsin(theta)?
The force applied is not perpendicular to r. In most fulcrum and board-string problems the forces do act at 90 , hence sin(90 ) = 1 and T = Fr.
How to solve fulcrum and boards on strings problems?
set Tclockwise = Tcounterclockwise. Be sure to include all torques, including the torque created by the mass of the board
What is the definition of systems NOT in equilibrium?
Any problem where the object in question has a non-zero acceleration, or net force, is a non- equilibrium problem
How to solve for systems not in equilibrium?
by setting the sum of the opposing forces equal to one another (FLeft = FRight ; FUp = FDown) but then add the term “ma” to the weaker side.
How to solve for equilibrium on an inclined plane?
The force down the plane due to gravity is always given by F = mgsin(theta). The force of friction is always parallel to the plane, but opposite the direction of the sliding motion. There will never be an acceleration perpendicular to the plane, so you can ignore these forces. After you have accounted for all possible forces, set the sum of the “down forces” equal to the sum of the “up forces” and solve for the unknown.
What is energy?
the capacity to do work
What is the formula for Kinetic energy?
KE= 1/2(mv)^2
What is the formula for gravitational potential energy?
–Gmm/r or mgh
What is the formula for elastic potential energy?
1/2kx^2
What is the formula for the electrical potential energy?
Kqq/r or qEd or qV
What is the formula for potential energy stored by a capacitor?
1/2QV or 1/2CV^2 or 1/2Q^2/C
What is internal energy?
The energy of the internal vibrations and random motions of atoms and molecules within a system. When non-conservative forces, such as friction or drag, act on a moving object they cause the conversion of some kinetic energy into internal energy.
What is heat and chemical energy?
heat - energy dissipated as heat
chemical - energy contained within chemical bonds, or energy stored/released due to the separation and/or flow of electrons
What is the formula for mechanical energy?
ME = KE + PE
In the absence of non-conservative forces such as friction, drag, air resistance, ____ is always conserved
mechanical energy
Name the type of energy possessed or created by: an explosion
Chemical energy turns into heat energy and the kinetic energy of any flying debris
Describe the energy transformations that take place as a rocket ignites, combusts its rocket fuel, launches into the air, rises to its maximum height, falls back to earth, and strikes the ground.
Chemical energy stored in the bonds of the rocket fuel is transferred into kinetic and gravitational potential energy as the rocket rises. If air resistance is taken into account some energy will also be dissipated as heat due to drag. Gravitational PE reaches a max at the max height and is then transferred back into kinetic energy (and heat if considering air resistance) as the rocket falls back to earth. When the rocket strikes the ground its kinetic energy is transferred into heat energy.
What is the Law of Conservation of Energy?
Energy is frequently transferred back and forth between forms, but never lost
What is an open, closed, and isolated system?
open - both mass and energy can be exchanged w the surroundings
closed - energy, but not mass can be exchanged
isolated - neither mass or energy can be exchanged
If energy is changed, think ____
WORK
1) Change in velocity (change in KE = work; this is the most common example)
2) Change in height (change in gravitational PE = work)
3) Change in position of masses/planets/etc. in space (change in gravitational PE = work)
4) Change in position of a charge (change in electrical PE = work)
5) Compression of a spring (change in elastic PE = work)
6) Friction (change in internal energy = work)
7) Air Resistance (change in internal energy = work)
What is the second way you should think of work?
W = Fdcosθ or Favgd
When is work positive? When is work negative?
positive - force and displacement are in same direction
(pushing a barbell upwards)
negative - force and displacement are in opposite direction
What is the first law of thermodynamics?
energy change is not always completely due to work; some energy is often lost to heat. Work and heat are the only two ways energy can be transferred into or out of a system.
What is the Work Energy Theorem?
If a net force does work on a rigid object, the work done on that object is equal to the change in the kinetic energy of the object.
W = KEfinal - KEinitial
How much work is done when a 1,000kg car traveling at 40 m/s applies its brakes and comes to a complete stop?
The work done is equal to the change in energy from the KE of motion at 40 m/s to zero KE at rest. KE = 1/2mv2 = (.5)(1,000)(40)2 = 8 x 105J.
What is the work done on a spring compressed by 0.5 meters? (k= 10N/m)
The work done is equal to the change in potential energy of the spring. PE = 1/2kx2 = (.5)(10)(.5)2 = 1.25 J.
What are simple machines?
reduce the amount of force necessary to perform a given amount of work. Machines never reduce or change the amount of work!
What is the formula for the force necessary to the work of the ramp?
Fm = mg(h/d)
h - height of the ramp
d - distance along hypotenuse
What is the formula for the force necessary to do the work of a lever?
Fm = mg(L1/L2) ; where L1 and L2 refer to the lever arms for the mass and the applied force,
respectively.
What is the formula for the force necessary to work a pulley?
Fm = mg/(# of vertical ropes directly lifting the mass)
What is the formula for the force necessary for the work of a hydraulic lift?
Fm = mg(h1/h2) or Fm = mg(A2/A1)
h1 and h2 - distances traveled by the large plunger and small plunger, respectively
A1 and A2 refer to the cross-sectional areas of the large plunger and the small plunger, respectively.
What are the 4 equations used for power?
1) P = ∆E/t
2) P = W/t
3) P = Fdcosθ/t
4) Pi = Fvcosθ
pi- instantaneous power - use when solve for power using force and velocity
When discussing electricity and circuits, positive charge is always a _____
lack of electrons
What is the charge of an electron?
e- = 1.6 x 10^ -19C
What is a conductor?
material that allows the flow of electrons through it relatively unimpeded
What is a resistor?
A resistor is a material that tends to impede the flow of electrons
What is an insulator?
a material with a very, very high resistivity
There is no perfect ideal insulator that allows zero current flow under all conditions. However, materials like glass and Teflon allow negligible current flow up to extremely high voltages
What is a semi conductor?
a material thought to be right in the middle of an insulator and a conductor
What is a super conductor?
material that under very precise conditions is thought to exhibit zero resistance to electron flow
What is an electric field?
An invisible influence that can exert a force on a mass or charge.
What are electric field lines?
always drawn with their tails at the positive charge pointing away or pointing toward the negative charge. Closer lines represent a stronger field; Lines further apart represent a weaker field.
Do field lines best approximate electron flow or current flow?
current flow, goes from positive to negative
electron flow (neg to positive)
What are equipotential lines?
These lines are drawn perpendicular to field lines and represent areas of equal voltage
What is an electric dipole?
A dipole is a separation of positive and negative charges of equal magnitude.
When the MCAT discusses dipoles they will either be two opposite charges of equal magnitude very near one another in space, or any object/molecule with a charge separation
A dipole that is NOT aligned w the electric field has ___ because alignment is a lower energy stat
potential energy
What is the difference between a point charge and constant electric field?
point charge - strength of field varies with distance from point charge
constant - strength does not vary w distance, voltage across the field is NOT constant
constant electric field equations are derived by comparison to ____
gravity near earth
point charge field equations are derived by comparison to ___
actual gravity
g (strength of gravitational field is equivalent to ___ in electricity?
E (strength of electric field)
G (constant) = ___
K (constant)
h (distance) = ____
r or d (both variables are used for distance in electric field equations)
m (mass) = ___
q (charge)
gh (gravitational potential) = _____
V (voltage, electrical potential)
What is the formula for point charge E-field?
F = Kqq/r2 (Coulomb’s Law)
Formula for a constant E-field
F = qE
How to find electrical potential energy for constant E-field
PE = qEd
How to find potential energy for point charge E-field
PE = Kqq/r
How to calculate voltage for constant E-field?
V = Ed (d measured against E)
How to calculate voltage for point charge E-field
V = Kq/r
In magnetism, replace positive charges w ___, and negative charges w ___
north, south poles
Magnetic fields are created by ___ and ___
changing electric fields, currents
What are examples of moving charges that create a magnetic field?
Nuclei with an odd atomic or mass number (because they exhibit nuclear spin)
Electrons (because they orbit and spin)
Current (because it is moving electrons)
Bar Magnets
What is the formula for the force exerted on a charged particle moving in a magnetic field
F = qvBsin(theta) ; where theta is the angle between v and B
UNITSofB=Ns/Cm or Kg/A*s^2=tesla(T)
Will north pole of a magnet attract or repel positivity charged particles?
No force is created between a static electric field and a static magnetic field. However, if the positively charged particles began to move then they would experience a force vector with a direction that could be determined using right hand rule—assuming that is, that the movement of the charges is NOT parallel to or 180 to the magnetic field vector.
What will be the effect when velocity slows to zero on the force experienced by a charged particle in a magnetic field?
According to F = qvBsin(theta), if velocity is zero there is no force. The charged particles must move within the magnetic field for any force to be created
The force exerted on a charged particle in a magnetic field is at maximum at what angle?
90 degrees with respect to the magnetic field vector
What is the direction of the vector for the magnetic field produced by a current-carrying wire with electrons flowing from right to left across this page?
rotating counter clockwise
thumb is pointing to right with current, and fingers curl counter clockwise
Current flows ___ to the direction of electron flow
opposite
What is current? Formula?
I = ∆q/∆t ; It is more intuitive to think of current as the amount of charge (i.e., electrons) that flows
past a fixed point per unit time.
Current moves from __ to __
Electrons flow from __ to __
current - pos to neg
electrons - neg to pos
What is the formula for resistance?
R = ρL/A ; where ρ = resistivity, L = length, A = cross-sectional area
For good conductors, it is generally true that resistivity __ linearly with temperature
increases
Explain on a molecular level why increased temperature increases resistance.
Increased temperature causes increased movement of the atoms in the conduit, increasing the average number of collisions an electron will have with atoms and therefore increasing resistance.
The wires between any two elements in a circuit are assumed to be ____
perfect conductors (resistance = zero)
What is voltage?
the amount of potential energy a system is capable of storing per unit charge (V = PE/q)
V = Ed and V = Kq/r
What is the formula for Ohm’s law?
V = IR
If voltage increases, and current remains constant, resistance ____ increase
CANNOT (Saying that increasing voltage will increase resistance if current remains constant, is rather like saying that increasing force while acceleration is held constant will increase mass)
What will happen if voltage is increased?
current will increase proportionally
What are capacitors? What is their symbol?
Capacitors store energy and charge by holding electrons on plates separated by a very small
distance.
Symbol - Two vertical lines of equal length
What is the formula for capacitance? Formula for PE stored by capacitor?
C = Q/V
U=1⁄2QV; U=1⁄2CV^2; U=Q^2/(2C)
What is the dielectric?
the substance between the two plates.
All capacitors have a dielectric, even if it is just air.
Increasing the dielectric strength, ___ capacitance
increases
The dielectric must always be a ____
Insulator; otherwise it would discharge the capacitor by allowing electrons to flow between the plates.
How does increasing or decreasing each of the following affect capacitance: plate area, plate thickness, distance between plates, strength of the dielectric and voltage?
plate area - Increasing plate area increases capacitance
plate thickness - no effect on capacitance
distance between plates - inverse
strength of the dielectric - increases
voltage - no effect
What is the symbol for a battery?
two unequal lines, longer line represents pos, short line represents negative terminal
What is the symbol of a resistor?
zig zag line
There is ALWAYS a ___ across any resistor when current flows through it
voltage drop
What is internal resistance?
Batteries experience internal resistance due to the resistivity of their internal components.
Current flow through parallel resistors is always apportioned ___ based upon resistance.
inversely
What is the symbol for a switch?
diagonal break in the line
For solving circuits using Ohms Law, you MUST have a ____ circuit
simplified
resistors in series are _____ together
added
For resistors in parallel, the total resistance is found how?
add the inverses of the resistance for each resistor, then take the inverse of that sum
1/Rtotal = 1/R1 + 1/R2 + 1/R3…
For capacitors in series, how do you find the total capacitors?
add the inverses of the capacitance for each capacitor, then take the
inverse of that sum
▪ 1/Ctotal = 1/C1 + 1/C2 + 1/C3…
With capacitors in parallel, how do you find the total Capacity?
add the capacitance of each capacitor directly
▪ Ctotal = C1 + C2 + C3…
In batteries in series, how do you find total voltage? In parallel?
series - add up voltages directly, current (amps) and capacity will stay SAME
parallel - add current and capacity directly , voltage will stay SAME
What are Kirchoff’s rules?
1st rule - total current into a node = total current out of a node
2nd rule - in any closed loop circuit, the sum of the voltages equals zero (the sum of the voltage drops across each resistor equals the total voltage of the battery)
Ohm’s Law across a resistor states that: Voltage drop across that resistor = _______
current through that resistor multiplied by the resistance of that resistor
What is the formula for electrical power?
P= IV
What is the difference between alternating current and direct current?
direct current - comes directly from battery (car power)
Alternate current - (household wiring) both polarity of voltage and direction of current periodically reverse.
Explain the terms “root mean square current” and “root-mean-square voltage” as they apply to household AC current.
(RMS) method of calculating both voltage and current are necessary for alternating current applications because the current and voltage over time are sinusoidal.
What is the intensity of a wave?
is a measure of power per unit area. Waves have power because they transport energy from one point to another in a given amount of time. Intensity is proportional to the square of the amplitude and the square of the frequency.
What is a phase of a wave?
is a relative measure of how closely two waves (typically with the same frequency) are oriented to one another in space, expressed in radians or degrees
How can waves be in the same phase?
In order to be 100% in phase, two waves would have to have the same frequency, wavelength, and timing of maxima/minima
Intensity is directly proportional to ___ and ___
amplitude squared and frequency squared
The units of intensity are __
W/m^2
What is attenuation?
The gradual loss of intensity as a wave passes through a medium. In non- dispersive mediums this is due to scattering (i.e., reflection) of some waves and absorption of wave energy
What is the formula for the intensity in decibels?
10*log(I/I0); where I is the intensity of the sound wave in W/m2 and I0 is the threshold of human hearing (I0 = 1 x 10-12 W/m2; which is usually given)
At a soccer match, the sound level rises from 20 decibels to 60 decibels. How much louder (more intense) is the sound at the end of this increase?
The difference between 20 and 60 decibels is 40 decibels, or 4 factors of 10. Therefore the sound intensity has increased by a factor of 10,000.
What is the difference between transverse and longitudinal waves?
Transverse waves cause disturbances perpendicular to their direction of travel (e.g., electromagnetic waves, a wave on a string)
Longitudinal waves cause disturbances parallel to their direction of travel (e.g., sound waves, p-wave earthquakes)
What are electromagnetic waves?
No medium required; capable of propagating in a vacuum; transfer energy and momentum through space (e.g., visible light, microwaves, radio waves, etc.)
What are mechanical waves?
Require a medium to propagate; cannot propagate in a vacuum; transfer energy in the direction of propagation, but do not transfer matter.
What is the formula for wave speed?
V=λf
What are the 3 cardinal wave rules?
1) Wave speed (velocity) is determined by the medium
2) Frequency never changes when a wave moves from medium to medium
3) Wavelength does change when a wave moves from medium to medium
What is the formula for wave speed?
v = sqrt(elastic/inertial).
The elastic property is often called a “modulus”. The inertial property is a type of density.
For velocity of a wave on a string, what is the elastic and inertial property of the formula?
elastic - tension
inertial - linear mass density
Increased tension always increases velocity. A thicker string (increased mass per length) always decreases velocity, provided the tension stays the same.
What is the elastic and inertial property of Velocity of sound waves in a gas?
elastic - bulk modulus (B)
inertial - density of the gas
velocity is also temperature dependent
What is the inertial and elastic properties of the velocity of sound waves in a solid?
elastic moduli are increased by larger factor than gas (sound compression waves)
What is the difference between constructive and destructive interference?
constructive - regions where amplitudes of superimposed waves add to each other (increasing amplitude)
destructive - regions where amplitudes of superimposed waves subtract from each other (decreasing amplitude)
What is a standing wave?
A standing wave exhibits no net transport of energy and does not itself propagate. In other words, there is no translational movement of nodes or antinodes.
What is beat frequency? What is the formula?
Occurs when two waves with close to the same frequency interfere.
▪ fbeat =/f1–f2/
What is the formula for the Doppler effect?
∆f/fs = v/c
▪ ∆λ/λs = v/c
v is RELATIVE velocity
c - 3x10^8 for light, 340 m/s for sound
In the Doppler effect, the greater the relative velocity, ___ the shift in frequency or wavelength
the greater
What will be the change in frequency due to The Doppler effect when the source and observer are traveling the same speed?
you don’t know the velocity of the source and the observer, so you could or could not have a Doppler shift
white light will shift __ (color) if the Doppler effect causes a perceived increase in frequency
blue
White light will shift ___ (color) if the Doppler effect causes a perceived decrease in frequency
red
sound is a ____ wave
mechanical
higher pitch sounds have __ frequencies, lower pitch sounds have __ frequencies
higher, lower
What is the difference between infrasound and ultrasound?
infrasound - frequency of sound too low for humans
ultrasound - frequency is too high for humans
What is resonance?
If the exact frequency at which the second object is caused to vibrate happens to be one of its natural frequencies
The frequency of any harmonic is equal to ___ frequency
n x fundamental frequency
What is the formula for harmonics of closed ended pipe?
L = nλ/2
What is the formula for the harmonics of an open ended pipe?
L = nλ/4
What is the 1st overtone?
the second harmonic is the 1st overtone
The 2nd harmonic is exactly ___ wavelength
one
What is the photoelectric effect and how does it relate to the particle model of light?
the observation that electrons are ejected from a material when light of sufficiently high frequency is used
What is the formula for the energy of a photon?
E = hf ; h = Planck’s constant E = hc/lambda
What is Young’s Double Slit Experiment?
The purpose of this slit was to create coherent wavefronts. Light traveled through the first two screens and formed alternating pattern of light and dark bands on the third screen.
What is the formula for Young’s double slit experiment?
x = λL/d
x- distance between fringes
λ - wavelength of light used
d - distance between 2 slits
L - distance between double slit and screen
What is diffraction?
the tendency of light to spread out as it goes around a corner or through a slit
During a Young’s Double Slit Experiment, how will increasing each of the following parameters change the distance between the bright fringes on the final screen : a) wavelength of light, b) distance between the two slits, and c) distance between the second and third screen?
a) increasing wavelength will increase the distance between fringes (x)
b) increasing the distance between slits (d) will decrease the distance between fringes (x)
c) increasing the distance between the second and third screen (L) will increase the distance between fringes.
longer wavelength = ___ frequency
lower (less energy)
shorter wavelength = ___ frequency
higher (more energy)
Order these waves of decreasing frequency: gamma rays, ultraviolet, radio waves, x-rays, microwaves, infrared, and visible light
gamma rays > x-rays > ultraviolet > visible light > infrared > microwaves > radio waves
What is the speed of light?
3.0 x 10^8 m/s
What is the wavelength range of visible light?
390-700 nm (ROY G BIV)
What is Snell’s Law?
the law of refraction of different mediums
n1sinθ1 = n2sinθ2
velocity of waves ___ in lower index mediums
increases
velocity of waves __ in higher index mediums
decreases
For total internal reflection to occur, the light must be passing from a ___ to a ___ medium
higher index to lower index
For waves of light passing from higher to lower index mediums, what is the critical angle?
the critical angle of incidence for which the angle of refraction is 90 degrees
plug in 90 for θ2 to solve for θ1 in Snell’s law to find critical angle
What is the difference between a real and virtual image?
virtual - There is no actual light emanating from or reaching the image (e.g., the image formed
behind a plane mirror)
real - There is actual light at the image (e.g., an image formed on your retina)
What is the difference between a converging and diverging lens?
converging - (a.k.a., convex, positive) = usually produces a positive, real, inverted image.
When the object is inside the focal point it produces a negative, virtual, upright image.
diverging - (a.k.a., concave, negative) = always produces a negative, virtual, upright image.
What is the difference between concave and convex mirrors?
concave - follow the same rules as converging lenses
convex - follow the same rules as diverging lenses
for plane mirrors, the image and the object will be ___ on either side of the mirror
equal distance
What is the formula for mirrors? lens equation?
f = 1⁄2r , 1/f = 1/di + 1/do
MUST use correct signs for every variable !!
What is the equation for magnification?
M = -di/do = hi/ho
What are the four lens/mirror rules?
1) Object distances (do) are ALWAYS (+)
2) Image distances (di) or focal point distances (f) are (+) if they are on the same side as the observer, and (-) if they are on the opposite side from the observer.
3) The observer and the object are on the same side for a mirror, and on opposite sides for a lens (You have to be behind your glasses to see through them!)
4) PRI / NVU: “Positive, Real, Inverted” and “Negative, Virtual, Upright”
What is the difference between near-sighted and far-sightedness?
near- The image is formed in front of the retina.
far - image is formed behind the retina
What is the formula for optical power?
P = 1/f
Does the power of the human eye increase or decrease when the ciliary muscles contract?
flexing of the ciliary muscles results in an increase in the curvature of the lens. As the curvature of a lens increases, its focal point decreases. Because power is the inverse of focal length, we know that a more curved lens (i.e., contracted ciliary muscles) produces a shorter focal point and therefore a more powerful lens.
Who has the more powerful lens, near-sighted or far sighted?
near-sighted
What is the formula for magnification of two lens systems? Formula for power?
Magnification: M = m1m2
Power: P= P1 + P2
