Particles and Radiation

Question 1

What is specific charge?

Answer 1

Charge/ mass

Question 2

What is an isotope?

Answer 2

Isotopes are atoms of the same element with different masses due to differing numbers of neutrons in their nucleus

Question 3

What is the strong nuclear force?

Answer 3

Force only experienced by hadrons
Exchange particles are gluons
Force is responsible for keeping protons and neutrons in the nucleus together
Attractive between 0.5 and 3 Fm and repulsive under 0.5 Fm

Question 4

What is Alpha decay?

Answer 4

Where a nucleus becomes stable by emitting an alpha particle. This consists of 2 protons and 2 neutrons

Question 5

What is beta minus decay?

Answer 5

Where a neutron turns into a proton. It emits an electron and an antineutrino

Question 6

What is beta plus decay?

Answer 6

Proton turns into a neutron. A positron and neutrino are emitted

Question 7

How was the existence of the neutrino hypothesised? Why is it needed?

Answer 7

Neutrino has no charge and negligible mass
Its existence was hypothesised to account in order to account for the conservation of energy in beta decay
Beta particles have a continuous range of energies. This is because the energy released in beta decay is shared between the beta particles (electron/ position) and the neutrino. There is a fixed amount of total energy for the decay, so the energy difference must be carried away by another particle

Question 8

What is a photon?

Answer 8

Fundamental particles that make up all forms of electromagnetic radiation
Photon is a mass less packet of electromagnetic energy
This means that energy is not transferred continuously but as discrete packets of energy

Question 9

What happens when a matter and anti-matter collide?

Answer 9

They annihilate each other to produce 2 photons which travel in opposite directions, in order to conserve momentum

Question 10

What are the four fundamental interactions?

Answer 10

gravity-
electromagnetic
strong nuclear
weak nuclear

Question 11

What are exchange particles?

Answer 11

When forces interact between two bodies, an exchange particle is passed between them. The exchange particle acts as the force carrier. It exists only for a few moments

Question 12

Describe the electromagnetic force

Answer 12

Acts on particle with charge. Infinite range. Virtual photons are the exchange particle.

Question 13

Describe the weak interaction

Answer 13

Limited to Beta plus/minus decay, electron capture and proton-electron collisions. W+ and W- bosons. Range 10*-18m

Question 14

Describe the strong interaction

Answer 14

Only affects hadrons. Pion is the exchange particle

Question 15

What are the two classes of hadrons? Give examples of each

Answer 15

Baryons- proton/neutron, and Anti-baryons (anti-proton/ anti neutron)
Mesons- pion, kaon

Question 16

What do all baryons decay into?

Answer 16

Proton

Question 17

What must be conserved in interactions?

Answer 17

Baryon number
Charge
Electron lepton number and muon lepton number
Energy and Momentum
Strangeness must be conserved in strong interactions, but can change by -1,0,+1 in weak interactions

Question 18

What do kaons decay into?

Answer 18

Pions

Question 19

Lepton examples

Answer 19

electrons, muons, neutrinos and their antiparticles

Question 20

Describe strange particles

Answer 20

Strangeness occurs if a particle contains a strange quark and is there to reflect strange particles are always produced in pairs.
Strange particles are produced through the strong interaction and decay through the weak interaction

Question 21

How to neutrons decay?

Answer 21

neutron to a proton, also produces electron and anti-neutrino

Question 22

Change of quark character in beta minus/plus decay

Answer 22

beta minus- down to up
beta plus- up to down

Question 23

What is the threshold frequency?

Answer 23

The minimum frequency of incident electromagnetic radiation required to remove a photoelectron from the surface of a metal.

Question 24

What is the work function?

Answer 24

The minimum amount of energy needed for an electron to be emitted

Question 25

What is the stopping potential?

Answer 25

The p.d. required to stop photoelectric emission from occurring. KeMax= eVs

Question 26

What is ionisation?

Answer 26

When an electron gains enough energy to be removed from the atom

Question 27

What is excitation?

Answer 27

When an electron moves to a higher energy level. This could be caused by:
Absorbing energy from collisions with other atoms/electrons
Absorbing a photon
A physical source, such as heat

Question 28

Explain how fluorescent tubes work?

Answer 28

A beam of electron flows from one end to another
These free electrons collide with orbital electrons in the mercury atoms
The orbital electrons gain energy and are excited to a higher energy level
They then return to ground state and UV photons are released
The electrons within the phosphorus coating absorb these photons are excited, then release visible light photons when they return to a lower energy level

Question 29

Line spectra

Answer 29

Line spectra is a phenomenon which occurs when excited atoms emit light of certain wavelengths which correspond to different colours
The emitted light can be observed as a series of coloured lines with dark spaces in between
Each element produces a unique spectra

Question 30

Emission spectra

Answer 30

emission spectrum contains a set of discrete wavelengths, represented by coloured lines on a black background

Question 31

Absorption spectra

Answer 31

white light passes through a cool, low pressure gas it is found that light of certain wavelengths are missing
An absorption spectrum consists of a continuous spectrum containing all the colours with dark lines at certain wavelengths
These dark lines correspond exactly to the differences in energy levels in an atom

Question 32

What shows that particles have wave like properties

Answer 32

Electron diffraction

Question 33

What shows that EM waves have particle like properties

Answer 33

Photoelectric effect.

Question 34

How and why does the amount of diffraction change when the momentum of the particle is changed?

Answer 34

Using deBroglie equation, when the momentum increases, wavelength decreases. This will mean the amount of diffraction decreases, and so the concentric rings of the interference pattern are closer together. (and vice versa)