Particle Physics

Question 1

What observation from the Rutherford scattering experiment provided evidence for the atom being mainly empty space?

Answer 1

Most alpha particles passed straight through

Question 2

What observation from the Rutherford scattering experiment provided evidence for the centre of the atom (nucleus) being charged?

Answer 2

Some alpha particles were deflected through very large angles

Question 3

What observation from the Rutherford scattering experiment provided evidence for the size of the nucleus being much smaller than the whole atom?

Answer 3

Very few particles were deflected through angles greater than 90 degrees

Question 4

What observation from the Rutherford scattering experiment provided evidence for most of the mass being concentrated in the nucleus?

Answer 4

A large mass would be required to deflect alpha particles at an angle greater than 90 degrees

Question 5

What were the main conclusions from the Rutherford scattering experiment?

Answer 5

• Most of the atom is empty space
• The nucleus at the centre of the atom is charged
• The nucleus is much smaller than the size of the whole atom
• Most of the mass of the atom is concentrated in the nucelus

Question 6

Why are high energies required in particle accelerators?

Answer 6

To overcome repulsive forces between particles

Question 7

Why do anti-particles produced in particle accelerators only survive for a couple of seconds?

Answer 7

They annihilate

Question 8

How do cyclotrons accelerate charged particles?

Answer 8

• There is an alternating pd/electric field
• This accelerates the charged particles between the dees
• The presence of a magnetic field causes the particles to move in a circular path
• As the velocity of the particles increases, the radius of the circular path increases
• The time for which the particle is in the dee remains constant

Question 9

What fields are used in a cyclotron and what are they used for?

Answer 9

• Magnetic field: force at right angles to create circular motion
• Electric field: accelerates particles to maintain circular motion

Question 10

What are the key features of the linac?

Answer 10

• Consists of a long straight tube containing a series of electrodes
• The charge on each electrode alternates between positive and negative
• Electrodes are connected to an alternating pd supply so the charge of each electrode is continuously changing between positive and negative

Question 11

How does a linac accelerate charged particles?

Answer 11

• The alternating pd supply and alternating electrodes means that the electric field between each pair of electrodes is constantly changing over time
• The alternating pd means the particle is always attracted to the next electrode along and repelled from the previous one

Question 12

Why does the length of each electrode in the linac increase?

Answer 12

To compensate for the increasing speed so that the particle stays in each one for the same amount of time

Question 13

How does thermionic emission work?

Answer 13

• When the surface of a metal is heated, its free electrons gain thermal energy
• When they have enough energy, they break free from the surface
• Once emitted, they can be accelerated using an electric field

Question 14

What accounts for the circular path of electrons in the electron gun?

Answer 14

• The magnetic force on electrons acts perpendicular to the plane containing B and v
• Therefore force acts towards the centre of the circle
• This provides a centripetal force on the electron that maintains circular motion

Question 15

How many quarks make up a baryon?

Answer 15

3 quarks or 3 anti-quarks

Question 16

What is the baryon number for a baryon?

Answer 16

1

Question 17

What is the baryon number for an anti-baryon?

Answer 17

-1

Question 18

What is the baryon number for a quark?

Answer 18

1/3

Question 19

What is the baryon number for an anti-quark?

Answer 19

-1/3

Question 20

What is the baryon number for a meson?

Answer 20

0

Question 21

How many quarks make up a meson?

Answer 21

2, a quark and anti-quark pair

Question 22

What is the charge of an electron and muon?

Answer 22

-1

Question 23

What is the charge of an electron neutrino and a muon neutrino?

Answer 23

0

Question 24

What quantities always have to be conserved in an equation for decay etc?

Answer 24

• Baryon number
• Mass-energy
• Momentum
• Charge
• Strangeness

Question 25

What is a bubble chamber and how does it show the presence of particles?

Answer 25

- Hydrogen kept in a liquid form above the normal boiling point at high pressure - Pressure suddenly reduced when a particle passes through and bubbles of gas form, showing a trail of ions - Particles with opposite charges curve in opposite directions

Question 26

What is a relativistic particle?

Answer 26

One travelling close to the speed of light, so a change in mass occurs

Question 27

What type of particle is a proton?

Answer 27

Baryon

Question 28

What type of particle is a neutron?

Answer 28

Baryon

Question 29

What type of particle is a pion?

Answer 29

Meson

Question 30

What type of particle is a kaon?

Answer 30

Meson

Question 31

What is the strangeness of a proton?

Answer 31

0

Question 32

What is the strangeness of a neutron?

Answer 32

0

Question 33

What is the strangeness of a pion?

Answer 33

0

Question 34

What is the strangeness of a kaon?

Answer 34

±1

Question 35

What do kaons decay into?

Answer 35

Pions

Question 36

What do pions decay into?

Answer 36

Muons

Question 37

What does a muon decay into, and how is this done?

Answer 37

Into electrons and anti-neutrinos via weak interaction

Question 38

What does an antimuon decay into?

Answer 38

Positrons

Question 39

What is quark confinement?

Answer 39

Quarks are never found in isolation, only in pairs or triplets

Question 40

What happens to quarks in beta decay?

Answer 40

A down quark turns into an up quark

Question 41

What happens to quarks in beta plus decay?

Answer 41

An up quark turns into a down quark