24 - Particle Physics

Question 1

Describe the alpha particle scattering experiment.

Answer 1

• Alpha particles fired at gold foil
• Scattered through 180 degrees
• Detected on fluorescent sphere by microscope

Question 2

What were the observations from the alpha particle experiment?

Answer 2

• Most particles were not scattered

- Only a very tiny amount were scattered more than 90 degrees

Question 3

What can we learn about an atom from the alpha particle scattering experiment?

Answer 3

• Most of an atom is empty space with dense mass at centre

- Nucleus is positively charged

Question 4

What is the average order of magnitude of the radius of a nucleus?

Answer 4

10⁻¹⁵

Question 5

What is the average order of magnitude of the radius of an atom?

Answer 5

10⁻¹⁰

Question 6

What is a nucleon?

Answer 6

A proton or a neutron

Question 7

What is the nucleon number?

Answer 7

number of protons and neutrons in the nucleus

Question 8

What is the top number (A) of a chemical notation?

Answer 8

Nucleon number

Question 9

What is the bottom number (Z) of a chemical notation?

Answer 9

Proton number

Question 10

How do we calculate the mass of an atom / nucleus?

Answer 10

Nucleon number x relative atomic mass (u)

Question 11

What does u stand for?

Answer 11

Relative atomic mass.

Question 12

What is the order of magnitude of density of a nucleus?

Answer 12

10¹⁷

Question 13

What is the order of magnitude of density of an atom?

Answer 13

10³

Question 14

Why must the strong nuclear force exist?

Answer 14

Because if it didn’t, the electrostatic repulsion between protons wouldn’t allow nuclei to exist.

Question 15

Describe the nature of the strong nuclear force.

Answer 15

• Acts over a very small range
• Repulsive up to 0.5 fm
• Attractive between 0.5 and 3 fm

Question 16

What is the order of magnitude of a fm?

Answer 16

10⁻¹⁵m

Question 17

What is an antiparticle?

Answer 17

A particle with the same rest mass as its particle version but the opposite charge.

Question 18

What happens when a particle and an antiparticle collide?

Answer 18

They annihilate.

Question 19

How do we symbolise an anti particle?

Answer 19

With a bar above the symbol.

Question 20

Rank the fundamental forces in order of strength.

(weakest to strongest).

Answer 20

Gravitational
Weak nuclear
Electromagnetic
Strong nuclear

Question 21

What is a fundamental particle?

Answer 21

A particle with no internal structure - it cannot be further divided

Question 22

What is a hadron?

Answer 22

A particle which is affected by the strong nuclear, weak nuclear and electromagnetic forces.

Made of quarks.

Question 23

Give three examples of hadrons.

Answer 23

Protons
Neutrons
Mesons

Question 24

What is a lepton?

Answer 24

A particle not affected by the strong nuclear force but affected by the weak nuclear and electromagnetic forces.

Question 25

Give three examples of leptons.

Answer 25

Electrons
Neutrinos
Muons

Question 26

What are hadrons made of?

Answer 26

Quarks.

Question 27

What is the name of a hadron made of 3 quarks?

Answer 27

Baryons

Question 28

What is the name of hadrons made of 2 quarks?

Answer 28

Mesons

Question 29

Describe beta minus decay.

Answer 29

Neutron decays into a proton, an electron and an antineutrino

Question 30

Describe beta plus decay.

Answer 30

Proton decays into a neutron, a positron and a neutrino

Question 31

What is always conserved in beta minus decay?

Answer 31

Nucleon number and charge

Question 32

Describe beta minus decay in terms of quarks.

Answer 32

A down quark decays into an up quark.

Question 33

Describe beta plus decay in terms of quarks.

Answer 33

An up quark decays into a down quark.

Question 34

Describe the quark makeup of a proton.

Answer 34

UUD

Question 35

Describe the quark makeup of a neutron.

Answer 35

UDD