phy unit 3 and 4

Kepler’s first law

all planets move about the sun in elliptical orbits with the sun as one of the foci

Kepler’s second law

a radius vector joining any planet to the sun sweeps out equal areas in equal lengths of time as the closer a planet the faster it moves and vice versa

Kepler’s third law

the square of the time it takes for a planet to complete an orbit of another body is directly proportional to the cube of the planet’s mean distance from the sun

Kepler’s third law equation

T²/r³=T²/r³ and T²/r³=4pi²/GM

electromagnetic wave

perpendicular electric and magnetic fields and do not need a medium, travelling at the speed of light in a vacuum

Einstein’s two postulates

1 - the laws of physics are the same in all inertial frames of reference

2 - the speed of light is constant in all inertial frames of reference

black body and example

object that absorbs and emits all radiation that falls on it so that no transmission or reflection occurs eg vantablack

double slit experiment

had light shining two thin slits making bright and dark spots on a screen behind the slits caused by constructive (bright) and deconstructive (dark) interference of light. the interference is a behaviour seen in mechanical waves thus providing evidence for wave nature of light

increase temp impact on intensity

increase intensity and amplitude of wave

Rutherford’s model

dense positively charged nucleus surrounded by orbiting neg. electrons

limitations of Rutherford’s model

1. charged particles radiate energy when they accelerate/orbit and thus should emit energy as they orbit nucleus eventually losing all energy and imploding, but doesn’t happen (why dont they spiral into nucleus

2. excited gas atoms emitted light in discrete lines not in continuous spectrum like expected (why electrons dont continuously emit energy and emission spectra only in discrete lines)

continuum expected spectra

all excited atoms where white light is diffracted through a prism

emission spectra (hot gas)

observed when light from excited atoms in gas state is diffracted through a prism and is unique for each atom

absorption spectra (cold gas)

weight is passed through cold gas and only specific wavelengths are absorbed and thus removed from the continuum

bohr model

electrons exist in fixed stationary states without emitting energy and electrostatic force pulls electron towards nucleus and e- intrinsic energy prevents from leaving state. electron absorb or emit photon with energy when change state

bohr model strengths and limitation

1. electrons dont emit energy in stable energy, thus dont continuously emit energy and wont spiral into nucleus

2. emission/absoprtion spectra explained by specific energies required to jump between energy levels - cannot accurately describe observation for multi-electron atoms, only predicted transitions for H (1-electron atom)

Lyman series

between n=1 and higher, ultraviolet light

Balmer series

between n=2 and higher, visible light

Paschen series

between n=3 and higher, infrared light

de Brogile

proposed that particles have an associated wavelength

fundamental particle split up

fermions - quarks and leptons

bosons - photon, gluon, w boson, z boson

quarks

up, charm, top (+2/3 charge) down, strange, bottom (-1/3 charge)

trend as increase in flavour

increases in mass and decreases in stability thus less time alive and more likely to degrade down to 1st flavour

leptons

electron, muon, tau (-1 charge), electron neutrino, muon neutrino, tau neutrino (0 charge)

baryon vs meson

baryon - made up of three quarks

meson - made up of one quark and one antiquark, charge must add up to an integer

antiparticles

anti up, anti down etc represented by dash and flipped charge (neg to pos) but no change in mass

photon (gamma symbol)

carrier of electromagnetic force passed between particles

gluon - only in quarks

mediate strong force, glues everything together eg” gluon hold two up quark together

w± boson

mediate weak nuclear force responsible for labour change like from u to d ± depend on beta decay

z boson

mediate weak nuclear force and charges

CPT symmetry conservations

translation symmetry - momentum

rotational symmetry - angular momentum

time symmetry - energy

electron-electron Feynman diagram

photon is instantaneously transferred between two electrons causing them to repel

electron-positron Feynman diagram

electron and positron collide and annihilate producing a photon temporarily before decaying into a new pair of electron and positron

proton-neutron beta pos. Feynman diagram

W+ boson created due to quark flavour change to maintain charge and then decay into positron and electron neutrino to maintain lepton no.

bha bha Feynman diagram

transfer for photon between positron and electron repel for some reason

flux density

flux/area - density of perpendicular mag field lines

faraday’s law

a change in mag field (mag flux) will produce an electric field (emf)

Lenz’s law

the direction of an induced electric current will oppose the change that produces it

explain why objects with mass cannot travel at the speed of light

due to relativistic momentum formula, if v=c the bottom of the fraction becomes 0 making momentum at c undefined and not possible. then W=F x s is the time derivative of momentum and if momentum is undefined at c, then F is also defined and thus work is also undefined and impossible to achieve

gravitational field

region of space around object within other objects with mass experience gravitational force of attraction

electric field

region of space around object within other objects with charge experience attractive or repulsive electrostatic force

zero vs max magnetic flux

zero flux - surface parallel to field lines, max flux - surface perp to field lines

electromotive force (emf)

diff in potential that gives a change in current=voltage

how is Lenz’s law match principle of conservation of energy

mechanical energy is converted into electrical energy to oppose charge

step down transformer

Vs<Vp, Ns<Np, current increases

muon problem and why it suggests newtonian physics is incomplete

cosmic rays colliding with particles at earth’s upper atmosphere producing muons that are unstable with short lifetimes. newtonian physics predict that it will decay high in the atmosphere but muons are detected on earth’s surface suggesting incomplete at speeds close to light due to time dilation observer on earth time is dilated and also experience length contraction allowing them to travel further in their reference frame

describe light as an electromagnetic wave

transverse wave doesn’t require medium made up of oscillating electric and magnetic fields perpendicular to each other

4 behaviours of light interacting with objects (incident radiation)

reflection, absorption, emission and transmission

blackbody radiation

emission of light (EMR) as a result of an object’s thermal energy

uv catastrophe

assumed that energy possessed and emitted by atomic oscillations had continuous values. blackbody radiation agreed with this at low frequencies but not as wavelength increased, predicting that blackbodies should radiate infinite energy

planck’s postulate

energy is emitted or absorbed in discrete packets called “quanta” not continuous emissions, meaning light can only exist at specific allowed frequencies

twins paradox

both twins observe that the other experiences dilated time. however, since space twin changes direction, they are no longer in inertial reference frame thus making their time slows down and making them the younger twin

ladder in a barn

from the barn’s perspective the ladder contracts to fit inside the barn shutting doors simultaneously when inside, but from ladder’s perspective the barn contracts making seemingly impossible to fit but doors do not close at the same time from ladder’s pov meaning it never has to be fully inside the barn at once

photoelectric effect

when a metal surface is illuminated by a high frequency light source, electrons can be ejected from the metal

work function

minimum energy required to eject electron from metal

what is a wave

transfer of energy from one location to another

wave-particle duality

proposes that all particles exhibit wave and particle characteristics, light is both at all times

how matter interacts with each other

exchanging bosons

fundamental particles

single points in space with no defined volume or internal structure

what happens to jump up or jump down energy level

jump up photon absorbed, jump down photon emitted

how experiments provide evidence of quantised photon nature

photoelectric experiment - photoelectrons only ejected when incident light above threshold frequency/work function, kinetic energy increases with light frequency

how do transformers work in terms of mag induction and faradays law

ac in primary causes change in mag field causing change in emf causing change in emf in second coil. emf is proportional to no. of coils and rate of mag flux change

weakest to strongest gauge bosons

gravity, weak, electromagnetic, strong