Physics II All Content

zeroth law of thermodynamics

any two systems placed in thermal contact will reach the same temperature (A=B, B=C, so A=C)

temperature

intensive quantity (independent of size)

filling a tire iwth air using ideal gas law

at first P = atm pressure and V inc. with n put into tire. once volume is constant, P inc. with n

ideal gases

volume dec. as pressure inc.

vapor pressure

pressure at which a gas coexists with its solid or liquid phase

proportional to temperature

partial pressure

pressure a gas would create if it occupied the total volume available

when vapor pressure exceeds partial pressure of water vapor,

water evaporates and ice sublimates

temp proportional to

vapor pressure

avg. KE

phase changes

energy enters/leaves the system without changing the temperature (Q=mL)

more energy required

to evaporate water below boiling point

steps of ice → steam

• Temp of ice rises (Q=mcT)

• At 0, ice melts (Q=mL)

• Temp of water rises (Q=mcT)

• At 100, water boils (Q=mL)

• When all liquid turns into steam, temp rises again (Q=mcT)

conduction:

heat transfer through stationary matter by physical contact

• Depends on cross-sectional area, material, thermal conductivity, and thickness

convection

• heat transfer by macroscopic movement of fluid

radiation

• electromagnetic radiation is emitted/absorbed

area of rectangle

change in v(P1-P2)

1st law of thermodynamics

E(int)=Q-W

Q

heat transfer into system

W

work done by the system

thermodynamic processes

- work = area under the curve

- Subtract work from total if going in negative direction

isobaric

constant pressure

- W = PΔV

isochoric

constant volume

- ΔV=0

- W=0

- E(int) = Q

isothermal

constant temperature

- E(int) = 0

- Q=W

- Reversible

adiabatic

no heat transfer

- Q=0

- E(int)=-W

- Temp dec. for expansion opposite for compression

- Reversible

2nd law of thermodynamcis

heat transfer occurs spontaneously from higher to lower temperature bodies only

carnot cycle

only reversible processes are used, most efficient

macrostate

- overall property of a system, no details provided

- Ex: total number of heads vs. tails

microstate

- detailed description of every element of a system.

- ex: order of heads/tails

entropy

amount of disorder in the system

T2

should be hotter temp for positive Q according to given equations

lower

electric fields always point towards the ___ potential

perpendicular

electrical field lines are ___ to equipotential surfaces

dielectric strength

amount of charge it can hold without breaking down

in series

1/C vs. R

same charge on each

total voltage is the sum of individual voltages (total voltage is distributed across the chain, acts like a voltage divider)

current only has one path

parallel

C vs. 1/R

same voltage on each

total charge is the sum of individual charges (total charge distributed across them, like dividers)

requires junctions in a circuit

current

rate of flow of charge

motion of electrons is opposite the current

equal

power supplied by voltage must always ___ power dissipated by resistor

Direct Current

charge flowers in one direction

const. V and I

alternating current

charge periodically reverses direction

sinosoidal voltage sources

reduces power loss when used for energy transmission

root mean squared

value/sqrt(2)

can use equations with this to find average power

terminal voltage

voltage measured across a source’s terminals

larger I or R = smaller

junction rule

total current into a junction equals total current out

loop rule

in any closed loop, energy supplied by sources equals energy lost in resistors

EMF (-) → (+) = add

EMF (+) → (-) = subtract

resistors in same direction as current: -IR

resistor opposite in direction to current: +IR

Voltmeter

measures voltage

parallel with device

same potential diff. as device

ammeter

measures current

in series with device

measure same current as flows through the device

galvanometer

measures V or I

needle swivels with change

for V: large R in series

for I: small R in parallel

potentiometer

measures emf without current

wheatstone bridge

add unknown resistor to circuit with galvanometer and two known resistors to find unknown resistance

magents

like poles repel, unlike poles attract

when broken, becomes two smaller version of it (poles cannot be separated)

magnetism

caused by moving charges

angle

with flux: between magnetic field and the n (perp to surface)

no flux: between magnetic field and velocity or position of object

Right Hand Rule: straight wire

thumb: current

magnetic field: fingers curled around the wire

Force: away from palm

Right Hand Rule: Coil/rectangle

thumb: magnetic field

fingers: curled in direction of current

force: away from palm

perpendicular motion

magnetic force perpendicular to velocity (think palm versus thumb)

force between parallel current-carrying wires

attractive if same direction

repulsive if opposite direction

induced emf

produced by changing magnetic field or change in magnetic flux

increases when change occurs more rapidly

induced current

effect of induced emf

creates a magnetic field that opposes the change in flux

if flux dec, B in same direction as it (ex: A dec.)

if flux inc, B in opposite direction (ex: A inc.)

flux

amount of magnetic field passing through coil (changes with movement)

electric generators

produce electricity by rotating a coil of wire in a magnetic field

convex (converging) lens with object outside focal point

real (on opposite side of lens from object): can be projected onto screen

inverted image (upside down, negative magnification)

where lines cross on other side of lens is where image is

if object is between 1f and 2f, image is larger

if object is beyond 2f, image is smaller

convex lens with object inside focal point

virtual (on same side as object)

upright image (upright, positive magnification)

magnified (larger image always)

where lines cross on same side of lens as object is where image is

object is between image and lens

concave (diverging) lens with objet inside or outside focal length

virtual (on same side as object)

upright image (upright, positive magnification)

smaller image always

power and focal length negative

image is in between object and lens

lens to fix nearsightedness (can see close but not far)

concave

far objects blurry

rays cross in front of retina (need to move onto retina so behind where it is now)

power should be negative (for concave lens)

lens to fix farsightedness (can see far but not close)

convex

close objects blurry

rays cross behind retina (need to move onto retina so in front of where it is now)

power should be positive (for convex lens)

nearsighted far point

anything beyond this point is blurry

distance of this is measured from eye to point

farsighted near point

closest distance where you have clear vision

distance of this is measured from eye to point

magnification

m > 1: image larger than object

m < 1: image smaller than object

m = 1: image is the same size

when measuring an electric field, could we use a negative test charge instead of a positive one?

a) no, electric fields can only be measured using positive test charges

b) yes, and the direction of the measured electric field would be the same as the force on the negative test charge

c) no, using a negative test charge would neutralize the electric field

d) yes, but the direction of the measured electric field would be opposite to the force on the negative test charge

d) yes, but the direction of the measured electric field would be opposite to the force on the negative test charge

a constant-volume gas thermometer contains a fixed amount of gas. which property of the gas is measured to indicate its temperature?

a) volume

b) pressure

c) density

d) mass

b) pressure

what is the temperature of ice immediately after it is formed by freezing water?

a) 0 because water freezes at this temperature under standard pressure

b) -1 because the ice may cool slightly below freezing point as it forms

c) 1 because the water might not have fully solidified yet

d) -5 because ice usually forms at a colder temperature than 0

a) 0 because water freezes at this temperature under standard pressure

a gas expands rapidly and no heat is exchanged with the surrounding. Its temperature decreases during this expansion. which explanation is correct in terms of the first law of thermodynamics?

a) the gas does work on the surroundings (W > 0) and no heat enters (Q = 0), so its internal energy decreases, leading to a lower temperature

b) the gas absorbs heat from surroundings (Q > 0) while doing no work (W = 0), causing the temperature to drop

c) the gas neither does work nor exchanges heat (Q = 0, W = 0), but its temperature drops spontaneously due to expansion

d) the temperature decreases because the internal energy increases as the gas expands, and temperature is inversely proportional to internal energy

a) the gas does work on the surroundings (W > 0) and no heat enters (Q = 0), so its internal energy decreases, leading to a lower temperature

is a temperature difference necessary to operate a heat engine?

a) yes, because work can only be produced when the working substance itself undergoes a temperature change during the cycle

b) no, because a heat engine can produce work even if the temperature is uniform throughout the system

c) yes, because a heat engine converts heat into work and this requires heat to flow from a high-temperature to a low-temperature reservoir

d) no, because a heat engine can extract energy directly from internal energy without any temperature difference

c) yes, because a heat engine converts heat into work and this requires heat to flow from a high-temperature to a low-temperature reservoir

If you wish to store a large amount of energy in a capacitor bank, should capacitors be connected in series or in parallel?

a) series, because the equivalent capacitance decreases, allowing higher energy storage

b) series, because the charge stored on each capacitor increases

c) parallel, because the equivalent capacitance increases, allowing more energy to be stored at a given voltage

d) parallel, because the voltage across each capacitor decreases, increasing total energy storage

c) parallel, because the equivalent capacitance increases, allowing more energy to be stored at a given voltage

why are equipotential lines (or surfaces) always perpendicular to electric field lines?

a) because electric field lines can only exist where the potential is constant

b) because moving along an equipotential line requires no work, so the electric field has no component along that direction

c) because electric field lines always follow the shortest path between charges

d) because equipotential lines represent regions of zero electric field

b) because moving along an equipotential line requires no work, so the electric field has no component along that direction

how can the motion of a charged particle be used to distinguish between a magnetic field and an electric field?

a) a magnetic field changes the speed of the particle, while an electric field only changes its direction

b) an electric field changes the speed of the particle, while a magnetic field only changes its direction (if the velocity is perpendicular to the field)

c) both electric and magnetic fields always change the speed of the particle

d) neither electric nor magnetic fields affect the motion of a charged particle

b) an electric field changes the speed of the particle, while a magnetic field only changes its direction (if the velocity is perpendicular to the field)

how can the magnetic flux through a surface be zero even when the magnetic field is not zero?

a) because the magnetic field is too weak to produce any flux

b) because the magnetic field is perpendicular to the surface, giving zero flux

c) because magnetic flux is only defined when the magnetic field is zero

d) because the magnetic field is parallel to the surface, so no field lines pass through it

d) because the magnetic field is parallel to the surface, so no field lines pass through it

why can a null measurement be more accurate than one using standard voltmeters and ammeters, and what limits its accuracy?

a) because a null measurement uses a galvanometer to detect zero current, minimizing loading effects; its accuracy is limited by the sensitivity of the galvanometer and the precision of known standards

b) because a galvanometer in a null measurement allows large current to flow for better readings; accuracy is limited by heating effects

c) because a galvanometer directly measures voltage and current more precisely than meters; accuracy is limited only by calibration

d) because a galvanometer eliminates all measurement errors in a null condition; accuracy is not limited by practical factors

a) because a null measurement uses a galvanometer to detect zero current, minimizing loading effects; its accuracy is limited by the sensitivity of the galvanometer and the precision of known standards

changing magnetic flux

induces an emf

back emf opposes induced emf

transformer

converts AC voltage to what the device needs

AC in primary coil produces changing flux, inducing AC voltage in secondary coil

if voltage increases, current decreases

step up transformer

output voltage (Vs) larger than input voltage (Vp)

step down transformer

input voltage (Vp) larger than output voltage (Vs)

Gauss’s law for electricity (maxwell equation)

electric fields originate on positive charges and end on negative charges (charge moves from positive to negative)

Gauss’s law for magnetism (maxwell equation)

magnetic field lines are continuous (no magnetic monopoles)

if you split a magnet, there is still one N and one S end

Faraday’s law (maxwell equation)

changing magnetic fields produce electric fields

change in flux induces an emf

Ampere-Maxwell law (maxwell equation)

magnetic fields arise from moving charges and changing electric currents

changing electric fields induce magnetic fields and vice versa

electromagnetic waves

oscillating electric and magnetic fields propagate as transverse waves

wavelength depends on oscillation period

frequency and wavelength are inversely proportional

carry energy away from their source

electric and magnetic fields are always perpendicular and in phase:

• when E = 0, B = 0

• when E peaks, B peaks

• E and B perpendicular to direction of propagation

reception

incoming EM waves accelerate electrons in antenna which is amplified and converted to images or sound

electromagnetic spectrum

Gamma: high E, short wavelength

• can ionize things due to high E

Radio: low E, long wavelength

• can only heat things due to low E

reflection

light bounces off

angle of reflection = angle of incidence

angled measured relative to the normal to the surface

smooth surface: specific angle to see

rough surface: see it from any angle

mirrors, water, telescopes

refraction

bending of light when it passes between different materials

refractive index: measures how a material refracts light

movement from high index to low index: bends away from normal

shorter wavelength (violet) bends more than longer wavelength (red)

lenses, prisms, optical fibers

critical angle

incident angle that produces theta2 = 90 degrees

if incident angle greater than critical angle: total internal reflection

• no refraction occurs (reflects 100% intensity into denser medium than refracting into less dense medium)

• travels from high index medium to lower index medium

lens

bends light rays due to refraction when light enters and leaves the material

axis of a lens: line passing through the center of the lens perpendicular to its surface

focal point

the point where the bent light rays from a converging/convex lens meet

focal length: distance from the center of the lens to the focal point

• shorter focal length, higher the power

image distance

positive for real images and negative for virtual images

Myopia (nearsightedness)

eye too long

lens too strong

need diverging lens

(-) power

create virtual image closer to eye within distance they can see

hyperopia (farsightedness)

lens too weak

eye too short

need converging lens

(+) power

create virtual image further from eye within the distance they can see

microscopes

two convex lenses:

• objective lens (further from eye): forms small real image

  • long focal length higher magnification

• eyepiece (closer to eye): magnifies small real image

  • image formed by objective becomes object for eyepiece

  • short focal length higher magnification

telescopes

collect more light than the human eye

two designs:

• convex objective and concave eyepiece (upright image)

• two convex lenses (common astronomical telescope)

distant objects

object distance is infinity (image forms at focal length of objective)

Chromatic aberration

occurs because different wavelengths focus at different points; can be reduced using multi-lens systems

• white light hits lens and reflected colors have different refractive index so different colors bend differently so they hit at different areas

Huygen’s principle

every point on a wavefront acts as a source of wavelets

wavelets spread forward at the same speed as the wave

the new wavefront is tangent to these wavelets

explains reflection and refraction