Particle Physics

Question 1

What are isotopes?

Answer 1

atoms of the same element with a different number of neutrons.

Question 2

what is specific charge?

Answer 2

charge divided by mass

Question 3

what is the strong nuclear force?

Answer 3

force that overcomes the electrostatic force of repulsion between protons in the nucleus.

Question 4

what is the range of the strong nuclear force?

Answer 4

3-4 fm

Question 5

what do alpha particles consist of?

Answer 5

two protons and two neutrons

Question 6

Why does beta radiation occur?

Answer 6

A neutron in a neutron rich nucleus changes into a proton. an electron and an anti-neutrino are also emitted as a result.

Question 7

Discuss the differences between alpha, beta and gamma radiation

Answer 7

alpha radiation is highly ionising and weakly penetrating. has a very small range pf a few centimetres. beta radiation is less ionising and more penetrating. it can pass through paper but is stopped by metal foil. Gamma radiation is weakly ionising but highly penetrating, it is stopped by thick lead.

Question 8

What is a photon?

Answer 8

a discrete packet of energy

Question 9

what is the equation for the power of a laser beam?

Answer 9

nhf

Question 10

What happens in annihilation?

Answer 10

a particle and anti-particle collide and two gamma photons are produced as a result.

Question 11

Why does positron emission take place?

Answer 11

when a proton changes into a neutron in an unstable nucleus with too many protons. A positron and a neutrino are emitted as a result.

Question 12

Describe pair production

Answer 12

a photon of sufficient energy can suddenly change into a particle anti-particle pair which then separates.

Question 13

What is the weak nuclear force?

Answer 13

the weak nuclear force causes a neutron to change into a proton in B decay and a proton to change into a neutron in positron emission.

Question 14

Draw Feynman diagrams for a neutron-neutrino reaction and a proton-antineutrino reaction.

Answer 14

See textbook

Question 15

Draw the Feynman diagram for electron capture, B decay and positron emission.

Answer 15

See textbook

Question 16

What are hadrons and leptons?

Answer 16

hadrons are particles that can interact through the strong iteraction and electromagnetic interaction if charged.
Leptons are particles that can interact through weak interaction.

Question 17

What are baryons and mesons?

Answer 17

baryons are hadrons, they are protons and all other hadrons that decay into protons.
mesons are hadrons that don’t include protons in their product decay.

Question 18

How many quarks make up a baryon?

Answer 18

3

Question 19

How many quarks make up a meson?

Answer 19

2

Question 20

In which interactions is strangeness conserved?

Answer 20

strong interaction

Question 21

Describe the photoelectric effect

Answer 21

when light above a threshold frequency is incident on a metal surface, electrons are emitted from the surface.

Question 22

What is the intensity of the incident radiation proportional to?

Answer 22

the number of electrons emitted per second.

Question 23

What is the work function of a metal?

Answer 23

the minimum energy needed by an electron to escape from the metal surface.

Question 24

What is the stopping potential?

Answer 24

the minimum potential needed to stop photoelectric emission from taking place.

Question 25

What is the photoelectric current proportional to?

Answer 25

the intensity of the incident light

Question 26

what is excitation?

Answer 26

the process of an absorbing energy without becoming ionised.

Question 27

why is the excitation energy always less than the ionisation energy?

Answer 27

because the electron isn’t locked completely out of the atom in excitation.

Question 28

How does the fluorescent tube work?

Answer 28

Ionisation and excitation of the mercury atoms occur as they collide with each other and the electrons in the tube. the mercury atoms emit UV photons during de-excitation. the UV photons are absorbs by the atoms of the fluorescent coating. the coating atoms then de-excite in steps and emit visible photons.

Question 29

What is the wave like nature of light?

Answer 29

light can be diffracted, refracted and reflected.

Question 30

What is the particle like nature of light?

Answer 30

the photoelectric effect

Question 31

Matter like nature of a particle

Answer 31

electrons can be deflected by a magnetic field.

Question 32

Wave like nature of a particle

Answer 32

a beam of electrons can be diffracted. They produce a pattern of rings on a fluorescent screen.