Section 1 - Particles and Radiation Exam Questions

Question 1

Describe how the strong nuclear force between two nucleons varies with separation (2)

Answer 1

Repulsive then attractive above 1 fm

Short range

Question 2

What is the nature of an alpha particle? (1)

Answer 2

Helium nucleus

Question 3

Define isotopes (1)

Answer 3

Same atomic number

Different number of neutrons

Question 4

Define nucleon number (1)

Answer 4

Number of protons and neutrons

Question 5

Define proton number (1)

Answer 5

Number of protons

Question 6

What term is used to describe an atom with one removed electron? (1)

Answer 6

Positive ion

Question 7

Why would an alpha particle outside the nucleus be unaffected by the strong nuclear force? (2)

Answer 7

Strong nuclear force has a short range

No effect at distances above 3fm

Question 8

Which constituent of an atom has the largest specific charge? (1)

Answer 8

Electron

Question 9

What is the term given to a photon being converted into an electron and a positron? (1)

Answer 9

Pair production

Question 10

Why is there a minimum energy for a photon to undergo pair production? (1)

Answer 10

Photon must provide enough energy to provide for the rest mass

Question 11

What happens to extra energy from a photon during pair production? (1)

Answer 11

Provides the formed particles with kinetic energy

Question 12

Which fundamental force is responsible for β+ decay? (1)

Answer 12

Weak force

Question 13

What occurs in positron emmision? (2)

Answer 13

A proton forms a neutron and gives out a W+ boson that then decays into a positron and electron neutrino.

Question 14

What is the virtual exchange particle used by electromotive force? (1)

Answer 14

Photon

Question 15

What are the three differences between the exchange particles for weak and electromagnetic forces? (3)

Answer 15

Photon is massless
Photon has infinite range
Photon does not carry charge

Question 16

Define an antiparticle (1)

Answer 16

All properties are opposite except mass

Question 17

State the quark composition of a meson (1)

Answer 17

Quark

Antiquark

Question 18

In weak decay, what property is not conserved? (1)

Answer 18

Strangeness

Question 19

Explain electron capture (3)

Answer 19

An orbital electron interacts with a proton in the nucleus, a neutron is formed and a neutrino is released.

Question 20

What roles can exchange particles have? (3)

Answer 20

Transfer energy
Transfer momentum
Transfer force

Question 21

What does a strange particle have different to a particle that is not strange? (1)

Answer 21

It contains a strange quark

Question 22

What is the most stable hadron? (1)

Answer 22

Proton

Question 23

State a difference between a muon and an electron (1)

Answer 23

Mass

Question 24

State a difference between hadrons and leptons (1)

Answer 24

Leptons do not experience the strong interaction but hadrons do

Question 25

What are the two hadron groups and the difference between them? (3)

Answer 25

Baryons and Mesons Baryons made from 3 quarks/antiquarks Mesons made from quark antiquark pair

Question 26

Why does the kinetic energy of emitted electrons have a maximum value? (2)

Answer 26

hf is energy available | Energy required to remove the electron varies

Question 27

If frequency of radiation is below a value, why are electrons not emitted? (2)

Answer 27

Work function is the minimum energy needed to release an electron Below a certain frequency, energy of a photon is less than work function

Question 28

As time delay for electron emission from a metal surface does not occur, how did this lead to a particle model for light? (2)

Answer 28

Light travels as particles | They transfer energy in discrete packets

Question 29

Explain what is meant by threshold frequency in reference to photon energy and intensity (3)

Answer 29

Threshold frequency is the minumum frequency for emission of electrons If frequency is below threshold frequency, no emission even if intensity increased because photon energy is less than work function.

Question 30

State and explain the effect on emitted electrons of increasing the frequency of incident light (2)

Answer 30

Maximum kinetic energy of released electrons increases | Because increasing frequency, increases photon's energy

Question 31

State and explain the effect on emitted electrons of increasing intensity of incident light (2)

Answer 31

Rate of electrons emitted increases | Because there are now more photons incident on the metal surface per second

Question 32

Define validated evidence (2)

Answer 32

Experiment needs to be performed | Results of experiment need to be repeatable

Question 33

Define ionisation of an atom (1)

Answer 33

When an atom loses an orbiting electron

Question 34

What happens to energy on electron impact of atoms in the ground state? (2)

Answer 34

Electrons can leave the atom | Electrons can be excited

Question 35

What happens to electrons in higher energy levels after ionisation? (3)

Answer 35

Orbiting electrons fall down To fill vacancy in the lower levels Photons emitted to take energy away

Question 36

Define ground state of an electron (1)

Answer 36

When electrons are in their lowest energy state

Question 37

Explain why only photons of certain frequencies cause excitation in a particular atom (4)

Answer 37

Electrons occupy discrete energy levels Need to absorb an exact amount of energy to move to a higher level Photons need to have a certain frequency to provide this energy All energy of photon absorbed

Question 38

Describe the process by which mercury atoms become excited in a fluorescent tube (3)

Answer 38

Electrons flow through the tube Electrons collide with mercury atoms Electrons in mercury atoms go up to higher energy levels

Question 39

What is the purpose of the coating on the inside surface of the glass in a fluorescent tube? (3)

Answer 39

Photons emitted from mercury atoms are in UV spectrum These photons are absorbed by the powder Powder emits photons in the visible spectrum

Question 40

What kind of experiment would confirm electrons have a wave like nature? (1)

Answer 40

Diffraction

Question 41

Why is it easier to demonstrate wave properties of electrons than of protons? (1)

Answer 41

Easier to accelerate electrons

Question 42

241/95 Am is produced from decay of 241/94 Pu, state the decay process responsible and explain (2)

Answer 42

Beta minus decay | No change in nucleon number and proton number increases by 1

Question 43

Explain why a smoke detector using americium-241 emitting alpha radiation poses no risk to the user (2)

Answer 43

Only a small quantity is needed | Alpha emitted only travels a few cm

Question 44

How it can be told that the weak force is responsible for a decay? (2)

Answer 44

Involves hadrons and leptons | Quark change occurs

Question 45

Photoelectric emission occurs from a certain metal plate when illuminated by blue but not red light, explain this (4)

Answer 45

Light consists of photons An electron in the metal absorbs a photon An electron needs a minimum energy to escape blue: hf > Ф red: hf < Ф

Question 46

Outline why wave theory of light fails to explain why blue light causes photoelectric emission and red light does not (2)

Answer 46

Every electron would gain sufficient energy from the waves in time No matter the frequency of the light

Question 47

Explain the role of exchange particles (2)

Answer 47

Force carrier | for four fundamental forces

Question 48

Name two exchange particles that mediate weak force (2)

Answer 48

W boson | Z boson

Question 49

Explain the process of pair production (2)

Answer 49

Photon interacts with an atom | Energy of photon creates particle antiparticle pair

Question 50

Explain why pair production cannot take place if the frequency of the photon is below a certain value (3)

Answer 50

Energy of photon depends on frequency If frequency is below a certain value, there is not enough energy To provide rest energy of particles

Question 51

When a sample of potassium-40 decays, the emitted β- particles have a range of energies from almost zero to a maximum value, Emax. Explain how this led Pauli to predict the existence of an unidentified particle (3)

Answer 51

Same energy released in each decay When beta less than max there is missing energy Must be another particle to carry away missing energy

Question 52

A discharge tube contains a gas at low pressure, a high pd is applied between electrodes in the tube. The gas becomes conducting and emits light. Describe how the charged particles causing conduction are produced (2)

Answer 52

Electrons pulled out of gas atoms so gas atoms become positive ions Conduction due to electrons and positive ions

Question 53

A discharge tube contains a gas at low pressure, a high pd is applied between electrodes in the tube. The gas becomes conducting and emits light. Explain why the gas emits light and why it is at low pressure (3)

Answer 53

Ions and electrons collide, recombine and emit photons Electrons excite gas atoms by collisions and photons are emitted on de-excitation Gas at low pressure so the particles are widely spaced

Question 54

In a discharge tube a high potential difference is applied across hydrogen gas in the tube. Discuss how the discharge tube is made to emit em radiation of specific frequencies. Explain why high pd is needed, discuss how energy level diagram predicts spectrum, show how one wavelength is related to two energy levels (6)

Answer 54

High pd: Pd accelerates electrons Electrons have to have sufficient energy to excite atoms Spectrum and energy levels: Visible spectrum results from excited electrons moving into lower level Each transition results in a photon of light Calculation: Energy difference equals E λ = hc/E matches spectrum