Physics 2 Flashcards
torque
T = Fl
T = mgl
T = Frsinθ → have to use when force isn’t applied at 90°
kinetic energy
KE = 1/2 m v^2
gravitational potential energy
PE gravitational = m g h
elastic potential energy
PE elastic = 1/2 k x^2
electrical potential energy
PE electrical = (k q1 q2) / r
potential energy stored in a capacitor
PE capacitor = 1/2 C V^2 = 1/2 Q V = (Q^2) / 2 C
internal energy
energy of internal vibrations and random motions of atoms/molecules
occur when non-conservative forces act on a moving object and cause conversion of some kinetic energy into internal energy
heat energy
energy dissipated as heat, usually dissipated from collision or in a current carrying wire
internal energy vs heat energy
often used interchangeably on the MCAT
chemical energy
energy contained within chemical bonds or energy stored / released due to separation and/or flow of e-
mechanical energy
ME = PE + KE
*** always conserved except in presence of non-conservative forces
work
W = ΔEnergy
W = Fdcosθ
W = Favg d
first law of thermodynamics
ΔE = W + Q
energy change is not always due to work, some is lost as heat
machines
never reduce the amount of work done
only change amount of force required to perform a given amount of work
ramps
Fm = mg (h/d)
h = height of ramp
d = distance along ramp’s hypotenuse
levers
Fm = mg (L1/L2)
pulleys
Fm = mg / (# of ropes directly lifting the mass)
of ropes directly lifting the mass = must lift the mass directly or lift a pulley that is attached to the mass
hydraulic lifts
Fm = mg (h1/h2)
Fm = mg (A2/A1)
h1 A1 = large plunger
h2 A2 = small plunger
power
- P = ΔE / t
- P = W / t
- P = Fdcosθ / t
- Pi = Fvcosθ
electric field lines
tails at positive charge, pointing to negative charge
represent current flow (opposite of e- flow)
closer lines = stronger field
equipotential lines
perpendicular to field lines
represent areas of equal voltage (electric potential)
electric force
constant E field → F = qE
point charge E field → F = kqq / r^2
electric field
constant E field → E = F/q or E = V/d
point charge E field → E = kq / r^2
electric potential energy
constant E field → PE = qEd
point charge E field → PE = kqq / r
magnetism
analogous to electricity ( + → north, - → south, field lines move north → south)
changing electric fields create magnetic fields and changing magnetic fields create electric fields
magnetic fields created by currents (moving charges)
magnetic force
F = qvBsinθ
magnetic field right hand rule
thumb = direction of current
curled fingers = magnetic field
magnetic force right hand rule
fingers = magnetic field
thumb = velocity
palm = magnetic force
current
flows opposite direction of e- flow
I = Δq / Δt
amount of charge (e-) that flows past a fixed point per unit time
resistance vs temperature
conductors: ↑ temperature (above room temperature) → ↑ resistivity
semiconductors: ↑ temperature (above room temperature) → ↓ resistivity
Ohm’s law
V = IR
*** if current is held constant and voltage increases, resistance doesn’t automatically increase, you would need to add more resistors to keep current constant
resistance
R = pL / A
p = resistivity
L = length
A = cross-sectional area
*** not dependent on current or charge
potential energy capacitor
PE = 1/2 C V^2
*** use C = QV to solve for missing variable
dielectric
substance between two plates of capacitor
*** always an insulator
↑ dielectric strength → ↑ capacitance
capacitance
C = Q / V
plate area vs capacitance
↑ plate area → ↑ capacitance
more surface area on inside of plate to store e-
plate thickness vs capacitance
plate thickness has no effect on capacitance → e- line up on inside surface of plates
distance vs capacitance
↑ distance between plates → ↓ capacitance
increased distance → increases voltage for a given Q on plates → decreases capacitance
voltage vs capacitance
↑ voltage has no effect on capacitance
↑ voltage increases charge stored but doesn’t increase capacitance (charge stored per voltage)
resistors in series and parallel
series: Rt = R1 + R2 + R3
parallel: 1/Rt = 1/R1 + 1/R2 + 1/R3
capacitors in series and parallel
series: 1/Ct = 1/C1 + 1/C2 + 1/C3
parallel: Ct = C1 + C2 + C3
batteries in series and parallel
series: Vt = V1 + V2 + V3 (current and capacity (Ah) stay constant)
parallel: add current/capacity (voltage stays constant)
Ohm’s law across single resistor
voltage drop across that resistor = (current through that resistor) x (resistance of that resistor)
intensity
power per unit area
units: W / m^2
I ∝ A^2 f^2
for light waves: I ∝ A^2
decibles
decible = 10 log (I/I0)
I0 = threshold of human hearing, 1 x 10^-22 W/m^2
electromagnetic waves
no medium required, can propagate through vacuum, transfer energy and momentum through space
transverse only
mechanical waves
require a medium, cannot propagate in a vacuum, transfer energy in direction of propagation
transverse (require stiff medium)
longitudinal (sound)
wave velocity
v = squareroot (elastic/inertial)
string: v = squareroot (T/u)
gas: v = squareroot (B/p) V proportional to squareroot of T
standing wave
no net transport of energy and doesn’t propagate
beat frequency
occurs when two waves with close to the same frequency interfere
f beat = I f1 - f2 I
color shifts
Doppler effect causes a perceived increase in frequency → white light will shift blue (perceived decrease in wavelength)
Doppler effect causes a perceived decrease in frequency → white light will shift red (perceived increase in wavelength)
pitch vs frequency
similar, pitch = perceived
higher pitch = higher frequency
lower pitch = lower frequency
harmonics equations
L = nλ/2 (string or pipe with matching ends—both nodes, or both antinodes) → gives all harmonics
L = nλ/4 (one node and one antinode; e.g., pipe open at one end only) → gives only odd harmonics
harmonics characteristics
the frequency of the first harmonic is called the “fundamental frequency
the frequency of any harmonic is equal to n*fundamental frequency
the 1st overtone is NOT the same as the 1st harmonic → second harmonic is the 1st overtone, the third harmonic is the 2nd overtone…
for oscillators with matching ends, the wavelength of the second harmonic equals the length of the string/pipe → λ = L
energy of a photon
E = h f
combine with c = f λ
Young’s double slit experiment
x = λL / d
x = distance between fringes
λ = wavelength of light used
d = distance between the two slits
L = distance between the double slit and the screen
diffraction
tendency of light to spread out as it goes around a corner or through a slit
electromagnetic spectrum
longer wavelength = lower frequency = less energy
shorter wavelength = higher frequency = more energy
visible light = 390-700 nm
index of refraction
n = c / v
n > 1 → medium more dense than air
Snell’s law
n1 sinθ1 = n2 sinθ2
*** frequency stays the same as it passes through different mediums, velocity and wavelength change
↓ n = ↑ velocity = ↑ wavelength
↑ n = ↓ velocity = ↓ wavelength
total internal reflection
light must be passing from a higher-index medium to a lower-index medium
critical angle = angle of incidence where angle of refraction would be 90°
images
virtual: no actual light emanating from or reaching the image
real: there is actual light at the image
mirrors
concave and convex mirrors follow the same rules as their respective lens
mirror equation
f = 1/2 r
r = radius of curvature (distance from mirror to center of curvature)
thin lens equation
1/f = 1/di + 1/d0
*** can use for mirrors too
magnification
M = -di/d0 = hi/h0
lens/mirror rules
- object distances (d0) are always +
- image distances (di) or focal point distances (f) are always + if they are on the same side as the observer and - if they are on the opposite side from the observer
- observer and object are on same side for mirror, observer and object are on opposite sides for lens
- PRI / NVU
*** apply to single-lens systems only
far-sighted
hyperopia
can focus clearly on distant objects, not on close objects
image forms behind retina
eye too short / lens too weak
correct with converging (convex) lens
near-sighted
(myopia)
able to focus clearly on close objects, not on distant objects
image formed in front of retina
eye too long / lens too strong
correct with diverging (concave) lens
two lens systems
M = m1 m2
P = P1 + P2
*** image formed by first lens becomes object for second lens
converging lens
usually produces a positive, real, inverted image
object is inside focal point → produces a negative, virtual, upright image
*** focal length is always positive (behind lens)
diverging lens
always produces a negative, virtual, upright image
*** always negative focal length (in front of lens)
optical power
P = 1 / f
*** ciliary muscle flexing → increased curvature → shorter focal length → increased power
diopter = 1 / f (m)
aberration
spherical aberration = light rays at ends of lens get bent more than ones closer to center
chromatic aberration = some colors get bent more than others (different index of refraction) → red gets bent less, blue gets bent more
e- charge
e- = 1.6 x 10^-19 C
electrical power
P = IV
voltage
(electric potential)
amount of work necessary to move a charge against an electric field
Voltage = Joules / Coulomb
constant E field → V = Ed
point charge E field → V = kq/r
Doppler effect
Δf / fs = v / c
Δλ / λs = v / c
c light = 3 x 10^8 m/s
c sound = 340 m/s
s = source
v = relative velocity
*** the greater the relative velocity the greater the shift of frequency/wavelength
critical angle
θC = arcsin(n2/n1)
