2: Particles and Radiation

Question 1

What can be used as evidence for discrete energy levels?

Answer 1

-Emission and absorption spectra as lines appear at discrete points
-Shows photons of specific frequency have been absorbed/emitted
-Shows electrons can only absorb an exact amount of energy to be excited

Question 2

How do we validate changes in the scientific community?

Answer 2

-Evaluated by peer-to-peer review
-This increases legitimacy and checks for errors

Question 3

How does a fluorescent tube work?

Answer 3

-High voltage is applied across mercury vapour which accelerate the free electrons
-The electrons then collide with the mercury atoms
-Mercury electrons are excited and move to higher energy levels
-Electrons then de-excite to release a UV photon
-Phosphorous coating absorbs UV photons and its electrons are excited and then de-excite to release visible light photons

Question 4

State a use of radioactive isotopes

Answer 4

Can be used to carbon date objects to estimate their age

Question 5

What is de Broglie wavelength?

Answer 5

Wavelength = Planck’s constant/Momentum
Diffraction occurs when wavelength and the distance of the gap are of the same order of magnitude

Question 6

What is wave particle duality?

Answer 6

The idea that light can be viewed as either a wave or a particle
Electron diffraction suggest wave behaviour due to interference pattern produced
Photoelectric effect suggests particle behaviour due to energy being dependent on frequency not intensity

Question 7

How do we calculate for line spectra?

Answer 7

hf=Ef-Es
Where Ef is the energy level an electron ends up at and Es is the energy level it starts at
To convert to eV multiply by (1.6)*10^-19

Question 8

What are emission spectra?

Answer 8

Lines showing various energy states an electron can occupy
An electron gains energy in a collision and is excited to a higher energy level
The electron then de-excites and releases a photon
Photons give up all energy, electrons only give up some

Question 9

How does the photoelectric effect work?

Answer 9

A photon collides with a surface electron and transfers its energy in a one to one interaction
The electron is then released if it has energy greater than or equal to the work function of the metal

Question 10

What are the exchange particles?

Answer 10

Electromagnetic: Virtual photon
Weak: W+/W-
Strong: Pion

Question 11

What is annihilation?

Answer 11

When a particle and its antiparticle equivalent collide to produce two gamma photons

Question 12

What is conserved in particle interactions?

Answer 12

-Energy
-Momentum
-Charge
-Baryon/Lepton number
-Strangeness(Only for strong)

Question 13

What is strangeness?

Answer 13

Only exists in kaons
Must be conserved only in strong interactions and can change in weak interactions

Question 14

What are leptons?

Answer 14

Leptons are fundamental particles
Muons are heavy electrons and decay into electrons

Question 15

What is pair production?

Answer 15

When one gamma photon splits to produce an electron and a positron

Question 16

What is a photon?

Answer 16

A particle used to represent light
Its energy equates to its frequency multiplied by Planck’s constant

Question 17

What is an antiparticle?

Answer 17

A particle with the same mass, same rest energy
But opposite charge and opposite lepton/baryon number

Question 18

Why was the neutrino proposed as a particle?

Answer 18

A range of energies were seen during beta-plus decay
The energy of the beta particle was fixed so an extra particle must be there to carry off the rest of the energy
This particle must be neutral charge to conserve charge

Question 19

What is beta minus decay?

Answer 19

The emission of an electron and production of an antineutrino
A neutron is converted into a proton

Question 20

What is alpha decay?

Answer 20

When a nucleus emits a particle consisting of two neutrons and two protons-equivalent to a helium nucleus

Question 21

What is the strong force?

Answer 21

A force that only affects hadrons
It is attractive up to 3fm and repulsive below 0.5-0.8fm
The strong force keeps the nucleus together

Question 22

Describe the composition of hadrons

Answer 22

A proton is uud
A neutron is udd

Mesons are a quark-antiquark pair
Pion0= up-antiup or down-antidown
Kaon0= down-antistrange or strange-antidown

Question 23

What are hadrons?

Answer 23

A group of particles consisting of baryons and mesons
Baryons are made up of three quarks and decay into protons
Mesons made up of a quark-antiquark pair and kaons decay into pions
Only hadrons experience the strong force

Question 24

What is an isotope?

Answer 24

An atom with the same number of protons/electrons but a different number of neutrons

Question 25

What is the work function?

Answer 25

The minimum amount of energy an electron must have to be released from the surface of a metal

Question 26

What is the threshold frequency?

Answer 26

The minimum frequency a photon must have to release an electron from the surface of a metal

Question 27

What is specific charge?

Answer 27

The ratio of the charge of a body to its mass

Question 28

What are the equations for the photo electric effect?

Answer 28

hf = Φ + Max Ek
hf = Φ + (1/2)mv^2
hf = Φ + e.Vs (stopping potential)

Question 29

Information that can’t be put on flashcards

Answer 29

-Model of an atom
-Feynmann Diagrams
-Nuclei notation
-Quark Quantities