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RSFC Physics > Section 1 - Particles and Radiation Exam Questions > Flashcards

Section 1 - Particles and Radiation Exam Questions Flashcards

Matter and Radiation, Quarks and Leptons, Quark Phenomena.

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1
Q

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

A

Repulsive then attractive above 1 fm

Short range

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2
Q

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

A

Helium nucleus

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3
Q

Define isotopes (1)

A

Same atomic number

Different number of neutrons

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4
Q

Define nucleon number (1)

A

Number of protons and neutrons

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5
Q

Define proton number (1)

A

Number of protons

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6
Q

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

A

Positive ion

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7
Q

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

A

Strong nuclear force has a short range

No effect at distances above 3fm

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8
Q

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

A

Electron

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9
Q

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

A

Pair production

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10
Q

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

A

Photon must provide enough energy to provide for the rest mass

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11
Q

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

A

Provides the formed particles with kinetic energy

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12
Q

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

A

Weak force

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13
Q

What occurs in positron emmision? (2)

A

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

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14
Q

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

A

Photon

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15
Q

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

A

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

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16
Q

Define an antiparticle (1)

A

All properties are opposite except mass

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17
Q

State the quark composition of a meson (1)

A

Quark

Antiquark

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18
Q

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

A

Strangeness

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19
Q

Explain electron capture (3)

A

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

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20
Q

What roles can exchange particles have? (3)

A

Transfer energy
Transfer momentum
Transfer force

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21
Q

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

A

It contains a strange quark

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22
Q

What is the most stable hadron? (1)

A

Proton

23
Q

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

A

Mass

24
Q

State a difference between hadrons and leptons (1)

A

Leptons do not experience the strong interaction but hadrons do

25
Q

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

A

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

26
Q

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

A

hf is energy available

Energy required to remove the electron varies

27
Q

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

A

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

28
Q

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

A

Light travels as particles

They transfer energy in discrete packets

29
Q

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

A

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.

30
Q

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

A

Maximum kinetic energy of released electrons increases

Because increasing frequency, increases photon’s energy

31
Q

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

A

Rate of electrons emitted increases

Because there are now more photons incident on the metal surface per second

32
Q

Define validated evidence (2)

A

Experiment needs to be performed

Results of experiment need to be repeatable

33
Q

Define ionisation of an atom (1)

A

When an atom loses an orbiting electron

34
Q

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

A

Electrons can leave the atom

Electrons can be excited

35
Q

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

A

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

36
Q

Define ground state of an electron (1)

A

When electrons are in their lowest energy state

37
Q

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

A

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

38
Q

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

A

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

39
Q

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

A

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

40
Q

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

A

Diffraction

41
Q

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

A

Easier to accelerate electrons

42
Q

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

A

Beta minus decay

No change in nucleon number and proton number increases by 1

43
Q

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

A

Only a small quantity is needed

Alpha emitted only travels a few cm

44
Q

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

A

Involves hadrons and leptons

Quark change occurs

45
Q

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

A

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

46
Q

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

A

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

47
Q

Explain the role of exchange particles (2)

A

Force carrier

for four fundamental forces

48
Q

Name two exchange particles that mediate weak force (2)

A

W boson

Z boson

49
Q

Explain the process of pair production (2)

A

Photon interacts with an atom

Energy of photon creates particle antiparticle pair

50
Q

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

A

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

51
Q

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)

A

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

52
Q

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)

A

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

53
Q

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)

A

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

54
Q

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)

A

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

RSFC Physics (13 decks)

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