Particles

Question 1

What are the main constituents of an atom?

Answer 1

Proton, Neutron, Electron

Question 2

What is meant by specific charge?

Answer 2

The charge to mass ratio: Specific charge = charge / mass (C/kg).

Question 3

What is the specific charge of a proton?

Answer 3

Specific charge = (1.6 × 10^-19) ÷ (1.67 × 10^-27) = 9.58 × 10^7 C/kg.

Question 4

What is the letter associated with a proton number?

Answer 4

Z.

Question 5

What is a nucleon?

Answer 5

A constituent of the nucleus: a proton or a neutron.

Question 6

What letter represents nucleon number?

Answer 6

A.

Question 7

What is an isotope?

Answer 7

A version of an element with the same number of protons but a different number of neutrons.

Question 8

State a use of radioactive isotopes.

Answer 8

Carbon dating – the proportion of carbon-14 can be used to estimate age.

Question 9

What is the strong nuclear force?

Answer 9

The fundamental force that keeps the nucleus stable by counteracting proton–proton electrostatic repulsion.

Question 10

Describe the range of the strong force.

Answer 10

Repulsive up to 0.5 fm. Attractive from 0.5–3 fm. Negligible past 3 fm.

Question 11

What makes a nucleus unstable?

Answer 11

Too many protons, neutrons, or both.

Question 12

How do nuclei with too many nucleons decay?

Answer 12

Alpha decay (emission of 2 protons + 2 neutrons).

Question 13

How do nuclei with too many neutrons decay?

Answer 13

Beta minus decay: neutron → proton via weak interaction (udd → uud).

Question 14

How was the existence of the neutrino hypothesised?

Answer 14

Beta decay seemed to lose energy. A neutral, near-massless particle must carry away this energy → neutrino.

Question 15

What is meant by beta minus decay?

Answer 15

A neutron turns into a proton, releasing an electron and an anti-electron neutrino.

Question 16

What is an alpha particle?

Answer 16

Two protons + two neutrons (same as helium nucleus).

Question 17

What is an antiparticle?

Answer 17

Same rest energy and mass as particle, but opposite properties.

Question 18

True or false: “Every particle has an antiparticle.”

Answer 18

True.

Question 19

What is the name of the antiparticle of an electron?

Answer 19

Positron.

Question 20

What is the antiparticle of π0?

Answer 20

π0 (it is its own antiparticle).

Question 21

What occurs when a particle and antiparticle meet?

Answer 21

Annihilation → converted to 2 gamma photons in opposite directions (conserves momentum).

Question 22

What is pair production?

Answer 22

A gamma photon converts into a particle–antiparticle pair.

Question 23

What is the minimum photon energy for a proton–antiproton pair?

Answer 23

2 × proton rest energy = 1876.514 MeV.

Question 24

Name the 4 fundamental forces.

Answer 24

Gravity, Electromagnetic, Weak nuclear, Strong nuclear.

Question 25

The virtual photon is the exchange particle of which force?

Answer 25

Electromagnetic force.

Question 26

What type of particles are affected by the strong nuclear force?

Answer 26

Hadrons.

Question 27

What is the exchange particle of the weak nuclear force?

Answer 27

W boson (W+ or W–).

Question 28

What does the electromagnetic force act on?

Answer 28

Charged particles (e.g. two positive charges repelling).

Question 29

When does weak nuclear interaction occur?

Answer 29

When quark character changes → affects all particles.

Question 30

Which properties must be conserved in particle interactions?

Answer 30

Energy, Charge, Baryon number, Lepton number, Momentum, Strangeness (only for strong interactions).

Question 31

What is a hadron?

Answer 31

Composite particle of quarks, held by strong force. Includes baryons and mesons.

Question 32

What are the classes of hadrons?

Answer 32

Baryons (3 quarks), Mesons (quark + antiquark).

Question 33

Pions and kaons are examples of which class?

Answer 33

Mesons.

Question 34

The pion can be an exchange particle for which force?

Answer 34

Strong nuclear force.

Question 35

What particle does a kaon decay into?

Answer 35

A pion.

Question 36

Give examples of baryons.

Answer 36

Proton (uud), Neutron (ddu).

Question 37

What is significant about a proton?

Answer 37

Only stable baryon. All baryons eventually decay into protons.

Question 38

What are examples of leptons?

Answer 38

Electron, Muon, Neutrino (and their antiparticles).

Question 39

What does a muon decay into?

Answer 39

Electron + two neutrinos.

Question 40

What is the strangeness of a strange quark?

Answer 40

–1.

Question 41

True or false: “Strangeness is always conserved in weak interactions.”

Answer 41

False. It is conserved in strong interactions. In weak interactions it can change by 0, –1, or +1.

Question 42

Complete the sentence: Strange particles are produced through the ________ and decay through the ________.

Answer 42

Produced via strong interaction, decay via weak interaction.