UWorld Physics, Uworld - Physics

Power (watts)

*P = W/t = ΔKE/t = ΔPE/t (mgΔh/t)*

cos(60º)

0.50

sin(45)

0.707

sin(60º)

0.87

square root of 3

1.73

thin lens equation

1/f = 1/o + 1/i ratio of image distance to object distance = ratio of image height to object height

µs

1e-6 s

visible spectrum

400 (blue) to 750 (red)

gauge pressure of fluid is 3, and fluid below has hydrostatic of 8, what is gauge pressure of lower liquid

8- 3 (gauge above) - 1 (atm) = 4 atm

how to find farenheight

9/5C + 32

Calorimetry question

A is correct, read analysis

continuity equation

A1v1 = A2v2, if area of vessel a =πr^2, so must square r

Kinetic friction analysis

Angle ↑ → K friction ↓ (perpendicular component decreases & parallel component increases).

flow and frequency in Doppler effect using ultrasound

As approach sensor, positive frequency shift, while negative velocity (flowing towards) As move away from sensor, negative frequency shift, while positive velocity (flowing away) Graph looks like -x graph, crosses origin

Bomb cell vs isolated calorimetry device

Bomb cell is housed in calorimtry device → exchanges heat with device to measure T change → closed system (not isolated). Caloimetery (in picture) is an isolated system with no heat exchange (*adiabatic*)

contrecoup injury

Brain inertia (Newton's 1st law) causes brain to keep moving even if the skull is stationary.

Heat transfer

By fluids movement (i.e. liquid nitrogen moving in tube) → ConVECTION from nitrogen to tube.

Capacitance and Area

C = A/d, increasing area increases capacitance

Capacitance

C = Q/v, units of farad

heat capacity (C)

C = mc, mass and specific heat C = mc = q/∆T q = C∆T = mc∆T q must be in kJ

molar heat capacity of gas

C at constant volume is less than that at constant pressure, because some energy is converted into gas, can be used to do work during expansion/compression of gas allowing piston to move freely to maintain constant P will increase molar heat capacity of gas

Combustion engine energy conversions

Chemical energy → thermal & KE

Power question

D

Velocity vs time graph

Displacement is area under curve.

energy and wavelength

E = hc/λ

energy and frequency

E = hf

Electric Field

E = ∆V/d, units of N/C

Force exerted in electric field

F = qE, charge x electric field strength

buoyant force

Fb = pVg density and displaced volume x 9.8

*Mechanical advantage:* Conservation of energy: *F1d1 = F2d2* Fidi = Fodo

Force output/ input = distance input/output. MA = 3/30 = 0.1

Pressure is equal to

Force/Area = N/m^2

mechanical advantage

Foutput/Finput = Dinput/Doutput

static friction

Fs = µs N friction is proportional to Fn, increasing angle of ramp increases perpendicular component of Fg, increasing Fn and frictional force

Ice melting and heat

Heat is 1st used to melt ice → no T change until ALL ice melts down. Heat then increases the temperature. If only water existed in the beaker, T would be higher (no heat used to melt ice)

Calorimetry question analysis

Heat lost by iron = heat gained by water. 1. q = mCAT for water (all variables given to find q) 2. q = mCAT for iron = q.water → find c for iron.

relationship between I and charge

I = Q/t

bouyancy

If buoyancy is floating, buoyancy = weight Fb = Fg, so Fb = mg, m = Fb/g does not depend on % of object submerged

resonant wavelength for open pipe

If open on both ends, L = lambda/2 closed end of pipe would have node (0 displacement). Open end has antinode (max displacement)

Kinetic friction question

Imagine both components. (A is correct)

average KE of individual gas molecule

KE = 3/2 kT, k = Boltzmann's constant, T = temp in K

what is absolute temp of gas directly proportional to?

KE of gas molecules

Friction question

Kinetic friction is proportional to the normal force (Fk = μkN), kinetic friction depends on an object's mass. It is INDEPENDENT of the object speed or surface area.

total magnification

M1 x M2 x ....

Torque

Maxes at 90 degrees and 0 at 0

Internal energy (U), heat (Q), pressure, volume *ΔU = Q + W*

No heat transfer → U = 0 Volume change by added pressure: *W = PΔV*

does hydrostatic pressure depend on area

No, P = pgh, area of flash has no effect

Is friction conservative?

No, distance matters not displacement even if ∆x = 0, work is not 0 as distance must be accounted for

power and energy

P = E/t, watts have units of J/s, watts x s = energy

Power as function of work and velocity

P = W/t = Fv

hydrostatic pressure

P = pgh, p = density, g= acceleration due to gravity, h = height

intensity of light wave

P/A = (E/t)/A, proportional to individual energy of each particle and # of particles emitted per unit time

Bernoulli's equation

PA+ ρghA+12ρ(vA)2= PB+ρghB+12ρ(vB)2

what equation is used to calculate pressure, given R constant

PV = nRT

volumetric flow rate

Q = Area x Volume, Q = mL/s Q = CO = ∆P/VR

charge in relationship to capacitance

Q = VC

Resistance of resistor

R = p x (L/A), p = resistivity, L = length, A = area resistivity is directly proportional to L and p

equivalent resistor in parallel

Rn = (Ra x Rb)/(Ra + Rb) Get normal equation, multiply by Ra and Rb, then take invert

lens strength

S = 1/f, if f = 2cm, 1/0.02 = 50 D

Lensmakers equatoin

S = 1/o + 1/I, o = distance from object, in case of eye, i = distance from lens, meaning distance from lens to retina in the eye

photon energy and frequency

Since E = hf, if E decreases (transfers energy to other thing), then f would also decrease

thermal conductivity of substance and temp

Substance that is more conductive feels colder - tile is more conductive than carpet, so heat transfer from body is more rapid and it feels colder

Thermal expansion

T↑ → L↑ αL=ΔL/ΔT

energy in circuits

U = 1/2 C V^2

volt equation

V = IR components in parallel have same voltage

velocity of light wave

V = c/n, decreases as N increases

voltage taking into account internal resistance

V = 𝓔 - Vr, 𝓔 = electromotive force, r = internal resistane changing resistance won't affect emf, but will decrease terminal voltage

what is N/C equivalent to?

V/m

Velocity vs time curve

Velocity = area under graph

finding work with ∆P

W = P∆V ∆U = Q + W, if no heat transfer (0 Q), then ∆U = W

equation for work

W = ∆PE = mh∆h must account for g

Units for C

W V, C s, V 𝛺 P = IV, I = P/V V = IR, I = V/R I = Q/t

power and mass relationship

W/∆T = ∆KE/t = mv^2/2t So power depends on mass

dielectric constnat

ability of dielectrics to increase capacitance, C = k x Cinitial increasing k increases C

lorentz force

accelerates moved charged particles in B field, depends on mass and inertia e- has less deflection than proton because of less mass

counting sig figs in number with lots of digits

all digits to right are significant 3.6180000 = 7 sigfigs

convex mirrors

always from upright virtual images

viscosity

amount of friction resisting motion, due to shearing forces between layeers if energy is put into fluid (stirring), will be dissipated by viscosity

partial pressure and length

as length increases (example along blood vessel), there will be more time for gas to flow through, so partial pressure will increase until it equilibrates

doppler effect

as sound source is closer to observer, new waves as moving towards observer, increase in observed frequency

Diffraction

bending of light around corners or narrow gaps

pressure drop across vessel

calculated from difference between pressure vessel and pressure of next vessel

closed system

can transfer heat with surroundings, such as bomb cell

where do cations move to

cations go towards cathode

doppler shift

compare f of source laser and given observed frequency source f = v/lambda laser f = c if source f = c, then no doppler shift, no movement and 0 velocity

gravity

conservative force, W =Fd, d being displacement if move object up, gravity does negative work

virtual images

convex mirrors (outward surface) forms images behind mirrors (virtual) concave mirrors (inward) forms images in front of mirror (real)

converging lens

create real and inverted images

diverting lenses

create virtual and upright images - virtual because light does not actually converge at the image

Magnetic field generation

current along straight wire = field lines moving lengthwise current along circular wire = unidirectional magnetic field, used in MRI's

current in series

current through each resistor is identical in series

attenuation

dampening of sound wave, decrease in amplitude (intensity) due to sound scattering sound attenuates most in soft materials attenuated as function of distance with inverse square law

venturi effect

decreasing speed of water will increase pressure

specific gravity

density of substance/density of water

fundamental frequency

depends on velocity and frequency of wave (lambda), as well as length of string

light properties with polarizers

designed to transmit light that is unrefracted and unreflected used with only transverse waves (light), because they cause oscillations perpendicular to direction of motion

stroke volume

difference in left ventricular volume at beginning and end of injection CO (volumetric flow rate) = SV x HR

diffraction grate

diffractive array with numerous slits of non zero width, bands help analyze components of wave front dark bands = destructive interference light bands = constructive interference don't use monochromatic light since don't need to use diffraction

electric field lines

direction that positive charge would accelerate in field point outward from positive charges, inward for negative charges

conductivity

ease that e- flow in substance, 𝜎=1/p, with p = R. Increasing conductivity decreases resistance, increasing current

photoelectric effect

ejection of e- from substance due to absorbance of emf waves, hf =1/2 mv^2 + W conservation of KE, increasing E will increase KE of ejected e-

M prefix

equal to 1e6, 5 MHz = 5e6

angle of incidence

equal to angle of reflection decreases as n increases

state function

equilibrium state of system as relationship between stuff, independent of path pressure, volume, temp, entropy

focal length of mirror

f = r/2, half of radius of curvature

wave speed on doppler shift

faster speed (light) results in smaller observed frequency shift (sound)

Lorentz Force

force exerted on ion in magnetic field F = q( E+ v(B)) in vector, F = cross product of V x B, so perpendicular

how do e- flow

from anode to cathode

emf waves in decreasing f and E

gamma, xray, UV, visible, infrared, micro, radio

capillary action

high adhesive forces (water to glass) than cohesive forces (Water to water) more surface tension would decrease capillary action

emf waves and temp

higher f are more energetic (E = hf), so have higher temp gamma waves have hotter radiation than microwave waves

calculating heat release in combustion

if combusting sample in water, heat released is absorbed by water q = m(of water) c∆T for value of C, need something with units of M and T, such as gram calorie (cal/g C)

when is total ME conserved

if only gravity is acting on it, spaceship launching from surface, total ME conserved so KE = PE

farsightedness

image if produced behind retina, corrective lens brings it closer to retina

nearsightedness

image is produced in front of retina, corrective lens moves it towards retina, away from lens

main source of peripheral resistance in blood flow

in arterioles, since they have the greatest rate of pressure drop

how to increase heat loss to environment

increase respiration, like dog panting

refractive index of light

increases with f, so violet light has more refraction than red

resistivity and area

increasing area provides more parallel channels current can flow through, causing less resistivity inversely proportional relationship

blood velocity and hydrostatic pressure

increasing velocity results in greater volumetric flow, decreasing blood hydrostatic pressure and filtration

relationship of sound intensity

inverse square, I = 1/r^2, increased area of spheres means intensity decreases exponential decay function

coffee cup calorimeter

isolated system, where heat and energy can't escape

isochoric

isovolumetric, no change in volume

what can cause bias

lack of validity, where value is not the true value

radius of curvature

larger if less affected in electric field, larger m/z ratio would mean less effect, causing larger radius of curvature

what type of wave is sound

longitudinal wave, molecules moving parallel to direction of propagation (like slinky)

units of volumetric flow rate (Q)

m^3/s

concave mirror with object outside f

make inverted, real image

concave mirror with object inside f

make upright, virtual image

surface tension and surface area

more surface tension water droplets would cause more spherical droplet, causing less SA compared to more flattened droplet

thin film interference

multicolored arrays, in system with 2 layers of semitransparent media intensity of colors depends on constructive/destructive interference, since fluid thickness isn't uniform surface tension or other effects that distort surface of fluid may cause light arrays

how to find magnification

multiplication (NOT ADDITION) of lens

maintain hydraulic pressure if work is double

must double cross sectional area of pipe

calculating tension

must keep in mind that T = Fg, so W = mg If tension is measured from lower half of body, then only account for half of body weight

Snell's law

n1 sin θ1=n2 sin θ2 entering higher refractive index (larger n) causes lesser degree of refraction (light bends towards normal)

adiabatic

no heat exchange

inverted electric field impact on torque

no impact, since sin(180) = 0

Ideal fluids

no viscosity, laminar flow (so equal velocity), incompressible

does medium of light affect energy

no, E = hf, not affected by medium

capacitance in parallel vs series

parallel = C1 + C2 + .... series = 1/C = 1/C1 + 1/C2 + ....

what to watch out for when calculating equilibrium concentration of gas

partial pressure of that gas

direction of magnetic force on moving ion without E field

perpendicular to ion's velocity and direction of magnetic field

hydrostatic pressure difference

proportional to density, gravity, and vertical displacement

problem with pressing incompressible fluid, measuring force exerted

ratio of force equal to area If 1/2 area, ratio of force is 1:2

Venturi effect

reduction of fluid pressure that occurs when flow velocity increases at constricted sections of tube

circular polzarization

rotation when 2 transverse waves propagate out of phase by 90º

influences on band pattern of diffracted light

slit width and wavelength

ideal behavior of gas occurs when

small molecular volume, low pressure, low interactions between molecules, high temp low pressure and high temp also serve to decrease interactions

sublimation

solid to a gas, like frozen nitrogen

center of mass

system of point masses, average of masses m weighted by displacement from fixed point If shifting mass (like shifting of fluid up in body), center of mass would also change

torque

t = rF, occurs in body joint, any sort of lever arm solve by making torque equal on both sides of fulcrum

how to find overall velocity

take resultant (root of squares) of component velocity

time to hit ground with initial vertical velocity

takes longer

inertia

tendency to oppose changes in motion depends on characteristics of object (mass), not gravity or position (external factors)

initial phase of research

to determine if question is valid

How to find exiting current

total of current entering, equal to V/R for both paths current exiting is twice the value of current entering if V and R are same for both sides

Kirchoff's rule

total potential difference around closed loop is 0

snells law if you don't have value of n

use c/v, since c = nv

shock wave ultrasound

use sound waves to deliver destructive, high amplitude vibrations to mess up targets frequency should match resonant frequency of target

if decrease area of tube by 1/2, how is v affected

v will double

sound as pressure wave

vibration of molecules results in oscillations of compressions (high pressure) and rarefactions (low pressure)

Voltage drop in parallel

voltage drop is equal across each resistor

how does ultrasound produce sound

voltage is applied, causes expansion and contraction of crystals - vibration produces sound because sound is form of pressure waves

effect of wavelength change if light is refracted

wavelength will change

sound velocity/intensity

when crossing mediums, portion of wave is reflect, losing intensity velocity increases with temp, and when moving from gas to liquid to solid

total internal reflection

when light leaves medium with high n, enters one with low n Incident angles greater than critical angle (90º), and light goes back into the medium instead of exiting

NiCd cells accepting current

will accept current from source until electrodes become pure, then reaction will stop and no more electrons will be accepted

if 2 people of different masses bounce on trampoline

will bounce the same height

area enclosed by cardiac PV loop is

work done by heart

Harmonic Wavelength equation

λn = 4L/n, n must be odd, closed end of pipe = node, minimum open end of pipe = antinode, max

uniform accelerated motion equation

∆X = VoT + 1/2 at^2

change in length due to thermal expansion

𝛼L∆T