Physics Flashcards
Define conservative force. List some examples.
CFs are derived from a POTENTIAL, path independent, do NOT dissipate the mechanical energy of the system
Ie. magnetic, electrostatic, gravity, elastic/spring
Define non-conservative force. List some examples.
NCFs do NOT derive from a potential, path-dependent, cause dissipation of mechanical energy of a system
Ie. friction, air resistance, viscous drag
Describe the difference between static vs kinetic friction force.
static: stationary, rolling w/o slipping
kinetic: sliding
Torque Equation
τ = rFsin(Θ)
When solving a kinematics problem involving projectiles, what are the TWO things you must keep in mind?
- There is an x AND y component! (Hence, don’t fall into the trap of only considering the vertical component!)
- Horizontal velocity (Vx) = constant, Vertical velocity (Vy) = only force acting on object is gravity (g), assuming no air resistance
Centripetal force equation
Fc = (mv^2) / r
Gravitational potential energy equation
U = mgh
Elastic potential energy equation
U = 1/2 k x^2
Work-Energy Theorem equation
Wnet = Delta(KE) = KEf - KEi
When net work is done on or by a system, the system’s KE will change by the same amount.
Work Equation
W = F • d = Fdcos(Θ)
Power equation
P = W (work)/t
in watts which is J/s
Isobaric: what is constant? What is 0?
PRESSURE (P) is constant
Delta(P) = 0
Isothermal: what is constant? What is 0?
TEMPERATURE (T) is constant
Delta (T) = 0 → Delta(U) = 0, where U = potential energy
Adiabatic: what does it mean? What is 0?
NO HEAT (Q) is exchanged Q = 0
Isochoric: what is constant? What is 0?
VOLUME (V) is constant (aka isovolumetric)
Delta(V) = 0 → Work = 0
Absolute pressure definition and equation
Ptotal = Po + ρgh
DEF: sum of all pressures at a certain point within a fluid, which includes the pressure at the surface of the fluid and the pressure due to the fluid itself
Gauge pressure definition and equation
Pgauge = P - Patm = (Po + ρgz) - P atm
DEF: the difference between absolute pressure and atmospheric pressure
Flow rate equation
Q = Volume / time = Av
A = cross sectional area v = velocity
Continuity equation (fluids)
Q = A1v1 = A2v2
A = cross sectional area v = velocity
Bernoulli’s equation
P1 + 1/2ρ(v1)^2 + ρgh1 = P2 + 1/2ρ(v2)^2 + ρgh2
DEF: sum of static pressure and the dynamic pressure will be constant between any two points in a closed system
Venturi effect (fluids): in a constricted area…
velocity ↑
static pressure ↓
Hydraulic lift equation
P = F1/A1 = F2/A2
F2 = F1(A2/A1)
Coulomb’s Law (Fe) equation
Fe = kq1q2 / r^2
signs of q don’t matter because abs value, but the sign of Fe matters because it is a VECTOR, so sign tells us about the direction and direction matters for Fe!
Electric field (electrostatic field) equation
E = Fe / q = kQ / r^2
Every charge generates an electric field, which can exert forces on other charges
Electric potential energy equation
U = KQq / r
Electric potential equation
V = U/q = kQ / r
The direction of U doesn’t matter (scalar), but the signs of the charges DO matter!
Moving point charge magnetic force equation
Fb = q v x B = q v B sin(Θ)
Current-carrying wire magnetic force equation
Fb = I L x B = I L B sin(Θ)
Magnetic field (B) of a STRAIGHT wire
B = µ0 I / (2πr)
Magnetic Field (B) of a loop of wire
B = µ0 I / (2r)
Current (I) equation, as well as its conventional vs real definition
I = Q / t
Conventional DEF: movement of POSITIVE charges from high → low potential
Reality DEF: movement of ELECTRONS that move in a circuit from LOW → HIGH potential
Capacitance (C) equation
C = Q (charge) / V (voltage)
Capacitance based on PARALLEL PLATE geometry
C = ε0 (A/d)
Electric field (E) in a capacitor equation
E = V / d
Potential energy (U) of a capacitor
U = 1/2 C V^2
Resistor (R) equation
R = ρL / A
ρ = resistivity L = length of resistor A = cross sectional area
In a series circuit, how do you calculate the total resistance? Total capacitance?
Rs = R1 + R2 + R3 +…+ Rn
1/Cs = 1/C1 + 1/C2 + 1/C3 +…+ 1/Cn
→ Cs = 1 / (1/C1 + 1/C2 + 1/C3 +…+ 1/Cn)
In a parallel circuit, how do you calculate the total resistance? Total capacitance?
1/Rp = 1/R1 + 1/R2 + 1/R3 +…+ 1/Rn
→ Rp = 1 / (1/R1 + 1/R2 + 1/R3 +…+ 1/Rn)
Cp = C1 + C2 + C3 +…+ Cn
Index of refraction (n) equation
n = c / v
c = speed of light (3x10^8 m/s) v = velocity
Snell’s Law equation
n1sin(Θ1) = n2sin(Θ2)
Critical angle (Θc) equation
Θc = inverse sin (n2/n1)
Θc is the angle in which total internal reflection (TIR) happens
What is specific gravity? What if you increase the density of the said fluid?
specific gravity = ρ(fluid) / ρ(reference fluid)
reference fluid is almost always water unless otherwise specified
↑ fluid density = ↑ specific gravity
Choose one: The object will float if the density of the object is (more/less) than the specific gravity of the fluid
LESS
What is the equation for hydrostatic pressure? What relationship do the variables have with each other?
P = ρgz
P = pressure ρ = density g = acceleration due to gravity z = depth
P is DIRECTLY, LINEARLY proportional to DEPTH (z)
ρ and g are just constants!
T/F: When calculating a question that provides you with the specific gravity of the fluid and the liters of fluid, you can find the mass by making ρ(water) = 1, and the mass you’ll find will be in g.
FALSE
THE MASS WILL BE IN FUCKING KG!!
Tank A and B are both 10 ft. The radius of tank A is TWICE of tank B. Each tank has equally sized holes of the same height. Which will the water flow out faster?
SAME
Since the radius of A is twice of B → MORE water (more mass) in A than B → MORE force in A than B = PRESSURE (F/A) IS SAME IN BOTH!!
So, Torricelli’s Law: v = sqrt(2gh) → velocity of water jutting out ONLY depends on the HEIGHT of the holes
→ since height of holes are same and the pressure of the tanks are the same = BOTH WILL FLOW OUT AT THE SAME RATE
How many L is in 1 cm^3?
1000 L
Alpha Decay
- equation
- What is emitted?
A/Z X → A - 4/Z - 2 (X - 2) + 4/2 He (2 p, 2 n, no e-)
emission of α particle, which is helium (aka 4/2 α, 4/2 He)
Gamma Decay
- equation
- what is emitted, and what does this result in as far as the parent nucleus is concerned?
A/Z X* → A/Z X + 0/0 γ
high-energy gamma rays (photons) → lower energy of parent nucleus WITHOUT changing atomic or mass #
ß- decay
- equation
- decay of ____ → _____
- What is emitted?
A/Z X → A/Z + 1 (X + 1) + 0/-1 ß-
neutron → proton
electron and antineutrino
ß+ decay
- equation
- decay of ____ → _____
- What is emitted?
A/Z X → A/Z - 1 (X - 1) + 0/+1 ß+
proton → neutron
positron (e+, ß+) and neutrino
If a question gave you the half-life and number of years (time) and asks you to find out what fraction of sample would remain, how would you solve this problem?
time / half-life = n (# of half lives) → (1/2)^n = answer
Ie. half-life of 30 yrs in 150 yrs
150/30 = 5 → (1/2)^5 = 1/32
The simple half-life equation
X’ = X(1/2)^n
n = # of half lifes
The complicated, exponential half-life equation
N = N0(e^-λt) OR N/N0 = e^-λt
N = remaining sample N0 = original sample e = 2.71 λ = 0.693 / t^(1/2)
According to the Doppler Effect, what happens to the wavelength and frequency a person perceives of the sound source when the sound source approaches closer to them?
↓ wavelength → ↑ frequency perceived
If f = actual frequency of moving sound source (ie. ambulance siren) and f’ = perceived frequency of the detector (ie. person), what would be the relationship between f and f’ before VS after the ambulance passes?
before: f < f’
after: f > f’
What is dispersion in light?
separation of light into different colors after passing through a prism due to refraction
Diffraction vs interference
diffraction: light spreading out after passing through a narrow slit
interference: light/dark patterns which represent constructive/destructive interference
What is: 10^-1 vs 10^1? 10^-2 vs 10^2? 10^-3 vs 10^3? 10^-6 vs 10^6?
deci vs deca (da)
centi vs hecto
milli vs kilo
micro (µ) vs mega (M)
What is:
10^-9 vs 10^9?
10^-12 vs 10^12?
nano vs giga (G)
pico (p) vs TERA (T)
T/F: Wave characteristics (ie. intensity) and the medium in which the wave moves both changes the speed of the wave
FALSE
ONLY THE MEDIUM, NOTHING ELSE!!
What is bulk modulus (B)? What is B a characteristic of? What happens to the travel speed of a wave when ↑ B?
the measure of medium’s resistance to compression
wave’s medium
↑ B = FASTER sound waves travel!
What happens to the travel speed of a wave when ↑ density of the medium?
↑ density = ↑ resistance to motion = ↓ speeds of sound
speed of sound wave equation that relates it with medium
v = sqrt(B/p)
B = bulk modulus p = density
T/F: As speed changes, the wavelength changes but f remains the same.
TRUE
Doppler effect equation. List what the sign changes mean for the detector and source when they move towards one another and away from one another
f’ = f [(v±vd) / (v-/+vs)]
In numerator:
If detector moves towards source → +
If detector moves away from source → -
In denominator:
If source moves towards detector → -
If source moves away from detector → +
“The pedestrian ALWAYS has the right of way” → the person is usually the detector and has the normal towards (+) and away from (-) as their signs.
→ JUST REMEMBER THAT SOURCE IS EXACTLY OPP!!
Equation that relates the velocity of sound with f and λ
v = fλ
what is the range of visible light? What is the approximate wavelength of red light? violet light?
400-750 nm
~700 nm
~400 nm
What is a closed pipe? What is the equation for the length of a closed pipe? What is the range of the harmonic number?
closed on one end, open on the other (ie. clarinet)
L = nλ/4 (L = pipe length, n = harmonic #, λ = sound wavelength)
n = 1, 3, 5… (ODD NUMBERS!)
What is an open pipe? What is the equation for the length of an open pipe? What is the range of the harmonic number?
open on both sides
L = nλ/2
n = 1, 2, 3…
From lowest to highest wavelength, rank all the waves in the electromagnetic spectrum starting with gamma waves to radio waves.
Gamma < X-rays < UV < visible Light < Infrared < Microwaves < Radiation
“Gate X Usually Lets In Most Radiation”
If a question asks you to find the ratio of the height between the object and its image, what is it asking you to find? How would you go about finding it?
magnification!!
m = hi/ho = di/do
- See what info they give you
- Find info they don’t give you (ie. If they don’t give you di, find it through the len’s equation)
- Do di/do = m = hi/ho!!!
Equation of lens power that relates with focal length
P = 1/f
Equation that relates the difference in intensities of 2 sounds
Delta dB (decibels) = 10 log (I / I0)
If = final intensity (aka I2) I0 = initial intensity (aka I1)
T/F: consecutive resonant sound wavelengths will differ in harmonic number by 2 in closed pipes.
TRUE
Harmonic numbers go 1, 3, 5… progress in 2s!!
What lens and mirror are considered converging systems?
convex lens
concave mirrors
What lens and mirror are considered diverging systems?
concave lens
convex mirrors
In converging systems (convex lens and concave mirrors), what would be the size, orientation, and/or reality of the image if the object distance was:
- do > 2f
- do = 2f
- 2f < do < f
- do = f
- do < f
do > 2f: Smaller, Inverted, Real (“SIR”)
2f < do < f: Bigger, Inverted, Real (“BIR”)
do < f: Bigger, Upright, Virtual (“BUV”)
“SIR BIRBUV”
do = 2f → same size (hi = ho) and di = do do = f → NO IMAGE (infinite magnification)
In diverging systems (concave lens and convex mirrors), what would the size, orientation, and reality of the image be like?
Smaller, Upright, Virtual
“SUV”
If transparent glass fiber optic cables transfer digital signals through light but you want to prevent light from exiting the transparent medium to minimize much loss of amplitude, what kind of characteristic is responsible for making this happen?
a) refraction
b) diffraction
c) reflection
d) dispersion
A
Reflection will help ensure the bouncing back of rays, which will prevent light from exiting the medium (refracting)
