Physics test 1

Convection

gaseous or liquid

the transfer of heat through the movement of fluids (liquids or gases) where warmer, less dense fluid rises and cooler, denser fluid sinks, creating circulating currents that distribute heat

conduction

the process by which heat or electricity is directly transmitted through a substance when there is a difference of temperature or of electrical potential between adjoining regions, without movement of the material.

layer of electrons that freely move, if you add heat they move faster

Pconduction

KATh-Tc/L

p is power

k is thermal conductivity

A is cross section of area

insulator

binds electrons

semiconductor

materials, commonly silicon, with electrical conductivity between conductors and insulators, acting as the foundation for modern electronics

steady state

rate of heat flow all the same thorughout material

number of moles

number of particles/Na N/Na

Na = 6.02×10²3 mol

mass of each particle

m particle N/m particle Na g/mol

Maxwell’s Distribution

describes the range of speeds of particles (atoms/molecules) in a gas at a specific temperature

change in p

pf-pi = 2mv

F =

mv²/l

root mean square speed

measure of average speed of particles in a gas

vrms= Sqrt of 3RT/M

internal energy is proportional to

temperature U= internal energy

this only applies to monotomic gases if a gas isnt monotomic there are other degrees of freedom -rotational and vibratinal KE that continue to internal energy U

Two containers of equal volume have the same number of moles of has and same temperature and pressure one is He and one is Ne

which rms speed is greater

Rms speed of neon atoms is less than that of the He atoms

atoms dont have the same speed only the same KE and internal energy

Thermodynamics

deals with the relationship between heat and other forms of energy

diathermal

heat can flow from surrroundinsgs to system

adiabatic

no heat can flow through from system to surroundigns

this is if heat takes so long to flow that there is neglibible exchange during observation time

zeroth law of thermodynamics

if two systems A and B are in thermal equilibrium with system C they are also in equilibirum with one another

condition of thermal equalibirum:

two systems are said to be in a thermal equilibrium if there is no heat flow between them when they are brought into contact

in deltaU = Q-W if Qand W are pos

Q+ = system gains heat

Q- = system loses heat

W+ = work is done by the system

W- = work is done on the system

if a gas gains heat without doing work on the surroudings or surrroundsings doing work on gas

the internal energt of the gas doesnt change

Joule’s experiment

use the faliing weight (grav PE) - convert into motion of paddles (KE)

work is done by gravity on the system

causes an increase in the T of the water

demonstrated the equivalence of mechanical work and heat, showing that mechanical energy (from falling weights turning a paddle) could be converted into thermal energy, raising the temperature of water, and forming the basis for the First Law of Thermodynamics

joules experiemnt proved that

mechanical energy (work) can be converted into heat

mehcnaical work can increase a systems internal energy just like direclty adding heat does

if has does work on its surroundings without exchaning nay heat the internal energy of the gas

decreases

U only depends on

the state of the system and not how energy enters the system

Q

energy transfer due to temp difference

W

energy transferred by a force moving adistance

thermal processes

specificies a way in which a systsem interacts with its surroudnings

quasi-static thermal process

one htat occurs slowly enough that a uniform temp and pressure exist thorughout

Isobaric process

occurs at constant pressure - an expansion of gas requires is transfer to keep pressure constant (if a gas under pressure expands without adding is the pressure will decrease)

W=PdeltaV

isobaric processes occur at constant pressure (

ΔP=0cap delta cap P equals 0

Δ𝑃=0

, typically with volume changes)

work done by system

Fs= P(change in distance) = P(change in volume)

W=P(Vf-Vi) Work under area P vs V curve

Area =

P(change in volume) = work

If you can figure out Area you can figure out work

if you compress piston, work is negative, but area is still positive

isochroic

process carried out at constnat volume

heat a gas in a closed container w= P(Vf-Vi)= 0 (does no work)

while isochoric processes occur at constant volume (

ΔV=0cap delta cap V equals 0

Δ𝑉=0

, meaning no pressure-volume work is done). Isobaric processes involve work (

W=PΔVcap W equals cap P cap delta cap V

𝑊=𝑃Δ𝑉

), whereas isochoric processes do not

Area under curve

delta U= Q (heat added) - coutn number of filled squares

As volume increases work

increases work done by system

when work is done on the system

theres negative area (vf-Vi)<0

isothermal process

occurs at constant temp deltaT=0 gas in contact with heat bath at constnat temp (need diathermal walls)

expansion

an expanding gas would cool down but the water bath supplies the extra heat needed

compressed isothermically

work done is negative

work done on the gas is compression so <0

isothermal delta U = 0

negative heat exchanged with environment

adiabatic process

no heat exchanged with. environment Q=0 gas insulated from surroundings

V, P, and T change

Q= 0

W= -delta U

adiabatic gas compressed

work done by gas is negative

change in internal energy is positive

heat exchanged is 0

Any process that decreases volume

has negative work

most internal energy

all paths are equal it doesnt matter how you get there

second law of thermodynamics

cold substance never gets colder by transferring heat to the hot surroundings

heat flows spontaneously from a substance of increased temperature to a substance of lower temperature but not vice cersa

akways hot to cold

all processes in nature are

irreversible

reversibility

ice getrs colder while surroundings get hotter (cannot happen)

heat engine

device that uses heat to perform work

1) heat is supplied at relatively high temperature from the hot resevoir

2) Part of the input heat is used to perform work by the working substance of the engine

3) The remainder of the input heat is rejected to the cold resevoir

heat engine variables

Qh=magnitude of iput

Qc = magnitude of rejected heat

W= magnitude of work done

heat enginge efficiency is defined as

the ratio of work done to the heat input

Eff = e= W/Qh

cyclic proces -

system returneed to the intial state after each cycle delta U

w=Q

eff = e = 1- Qc/Qh

some of the work done must be used to dissapate

other forces (friction resistance, etc)

work is ultimately converted into heat loss to the environment and it cannot be recovered

this limits the efficiency of an engine

idealization

carnot engine operates reverisbly so no heat loss

both. the system and environment can be returned to og state

1-Qc/Qh = 1-Tc/Th

carnots staetment of 2nd law

that no heat engine operating between two temperature reservoirs can be more efficient than a reversible Carnot engine operating between the same temperatures, and all reversible engines between those temperatures have the same maximum efficiency

There is a fundamental limit tothe max efficiency of any heat engine

e<ec= 1- Tc/Th

even a carnot engine cannot reach 100% efficiency it would require Tc to be 0K

the cold resevior must have a finite temp

Refridgerators and Ac are heat engines in reverse

work is done on the system

it is possibel for heat to be converted to work

spontaneous heat flow occurs from hot to cold and no work is donw

entropy

when a system goes from an ordered to a less ordered state it increases in entropy

fundamentally related to 2nd Law

state function for a given system macroscopic property the same way that T, V, P and U all are - only depends on initial and final states

S= klogW

entropy increaes whenever heat is

gained and decreaes when heat is lost s= q/t

for a carnot engine

entropy of a hot reseviro will decreases and entorpy of the cold will increase by same amount

real engine entropy

gain of cold resevoir will always be more than entropy lost of heat resevoir

Reversible S=0

doesnt alter the entropy of universe

Irreversible entropy

S>0

2nd law says that the entropy of hte universe is

always increasing

In context of the 2nd law of thermo the increase in entropy of a system

is related to the availability of energy to do work

Tc to Th less work lower efficiency

Irreversible thermo processes increase the

entropy of the universe and decrease the avaiable energy to do work

increase temperature of surroundings

Wunavail there is less overall energy to do work

heat death is an inescapable consequence of 2nd law of thermo

breaking glass goes back to original state

reversible process this violates 2nd law of thermo

gravity at work

attractive forces between masses scale solar systems and galaxies

electromagnetism

force between particles with electric charge and hold atoms together

strong vs weak force

strong - force between quarks and holds nuclears together

weak - short range froce and responsible for radioactivity

coulomb force

analogous to mass for gravitational force

charge comes in two opp types pos vs neg

signs of the interacting charges determine the direction of electrical force on matter

fractional charges (quarks)

make up protons but are not observed free in nature

electrical charge is conserved

Law of conservation of charge

the NET charge of an isolated system is constant

creation of matter from energy occurs in pairs of opposite charge

annihilation of matter also occurs in pairs of also opp charge

macroscopic objects charge is carried

by electrons protons don’t move

carnot engine hypothetical and reversible

doesnt have any net entropy

charge is a property of a particle that determines

whether it interacts electromagnetically

electrical charged in quantized

smallest unit of charge is observed in nature

insulators

electrons are bound tightly to parent atom and cannot freely dissociate

cahrge remain localized and doesnt move freely

wood

semi conductors

silicon

materials that are intermediate between conductors and insulators. they allow charge to flow under certain conditions someitmes only in 1 direciton

conductors

electrons are bound loosely to prevent atoms can freely dissociate from it

charges move freely

metals water

superconductor

no hinderances normally macroscopic objects are neutral

add or remove electrons through

direct contact

rub with cloth electrons from the contact surface of the cloth stick to the balloons/rods (doesn’t work on a humid day bc water molecules in air interfere and neutralize charge)

triboelectric series

induced charges (redistribution) - induce localized charge on an isolated conductor

move a charged rod nearby (no contact with rod)

charge is locally redistributed (seperation of ++ charges)

consequece of mobility of cahrges in conductors

charges electrons move away from net negative cahrge

no net chrage added (water/rod) remains electrically neutral

charging a conducting sphere by contact

negatively charged rod: electrons transferred direclty to the sphere during contact

conducting sphere (isolated system) is left with a net negative charge

number of moles =

number of particles over avogadros number

pressure final minus inital =

2mv

F=

mv²/L

f=

N/3 (mv²rms/L)

Bigger atoms are

slower than smaller atoms

IF a gas gains heat without doing work on its surroudnings or the surroudnings doing work on the gas, the internal energy of the gas

increases

If a gas does work on its surroiundings wihtout exchanign any heat the internal energy of hte gas

decreases

If rod is positively charged

electrons move to the rod during contact

spherical conductor

excess charge ends up uniformly distributed over the surface

coulombs law

direction radial inward (attractive) or radially outward (repulsive)

coulombs force is much bigger than grav force

graivty is negligible

forces are vectors

you must always consider the direction with each force pair - in 1D this is a + or - sign it is a vector in the plane of the charges in 2D

normally macroscopic objects are neutral

add or remove electrons through direct contact

rub with a cloth; electrons from the contact surface of the cloth stick to the balloons/rods

electric field

a charge or charge distributed located at the origin (and fixed in a place)

use a test charge and g0 which is moved around to every point in teh vicinity of the charge distribution

the force on g0 gives the direciton of energy