Section 1 - Particles and Radiation Exam Questions Flashcards
Matter and Radiation, Quarks and Leptons, Quark Phenomena.
Describe how the strong nuclear force between two nucleons varies with separation (2)
Repulsive then attractive above 1 fm
Short range
What is the nature of an alpha particle? (1)
Helium nucleus
Define isotopes (1)
Same atomic number
Different number of neutrons
Define nucleon number (1)
Number of protons and neutrons
Define proton number (1)
Number of protons
What term is used to describe an atom with one removed electron? (1)
Positive ion
Why would an alpha particle outside the nucleus be unaffected by the strong nuclear force? (2)
Strong nuclear force has a short range
No effect at distances above 3fm
Which constituent of an atom has the largest specific charge? (1)
Electron
What is the term given to a photon being converted into an electron and a positron? (1)
Pair production
Why is there a minimum energy for a photon to undergo pair production? (1)
Photon must provide enough energy to provide for the rest mass
What happens to extra energy from a photon during pair production? (1)
Provides the formed particles with kinetic energy
Which fundamental force is responsible for β+ decay? (1)
Weak force
What occurs in positron emmision? (2)
A proton forms a neutron and gives out a W+ boson that then decays into a positron and electron neutrino.
What is the virtual exchange particle used by electromotive force? (1)
Photon
What are the three differences between the exchange particles for weak and electromagnetic forces? (3)
Photon is massless
Photon has infinite range
Photon does not carry charge
Define an antiparticle (1)
All properties are opposite except mass
State the quark composition of a meson (1)
Quark
Antiquark
In weak decay, what property is not conserved? (1)
Strangeness
Explain electron capture (3)
An orbital electron interacts with a proton in the nucleus, a neutron is formed and a neutrino is released.
What roles can exchange particles have? (3)
Transfer energy
Transfer momentum
Transfer force
What does a strange particle have different to a particle that is not strange? (1)
It contains a strange quark
What is the most stable hadron? (1)
Proton
State a difference between a muon and an electron (1)
Mass
State a difference between hadrons and leptons (1)
Leptons do not experience the strong interaction but hadrons do
What are the two hadron groups and the difference between them? (3)
Baryons and Mesons
Baryons made from 3 quarks/antiquarks
Mesons made from quark antiquark pair
Why does the kinetic energy of emitted electrons have a maximum value? (2)
hf is energy available
Energy required to remove the electron varies
If frequency of radiation is below a value, why are electrons not emitted? (2)
Work function is the minimum energy needed to release an electron
Below a certain frequency, energy of a photon is less than work function
As time delay for electron emission from a metal surface does not occur, how did this lead to a particle model for light? (2)
Light travels as particles
They transfer energy in discrete packets
Explain what is meant by threshold frequency in reference to photon energy and intensity (3)
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.
State and explain the effect on emitted electrons of increasing the frequency of incident light (2)
Maximum kinetic energy of released electrons increases
Because increasing frequency, increases photon’s energy
State and explain the effect on emitted electrons of increasing intensity of incident light (2)
Rate of electrons emitted increases
Because there are now more photons incident on the metal surface per second
Define validated evidence (2)
Experiment needs to be performed
Results of experiment need to be repeatable
Define ionisation of an atom (1)
When an atom loses an orbiting electron
What happens to energy on electron impact of atoms in the ground state? (2)
Electrons can leave the atom
Electrons can be excited
What happens to electrons in higher energy levels after ionisation? (3)
Orbiting electrons fall down
To fill vacancy in the lower levels
Photons emitted to take energy away
Define ground state of an electron (1)
When electrons are in their lowest energy state
Explain why only photons of certain frequencies cause excitation in a particular atom (4)
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
Describe the process by which mercury atoms become excited in a fluorescent tube (3)
Electrons flow through the tube
Electrons collide with mercury atoms
Electrons in mercury atoms go up to higher energy levels
What is the purpose of the coating on the inside surface of the glass in a fluorescent tube? (3)
Photons emitted from mercury atoms are in UV spectrum
These photons are absorbed by the powder
Powder emits photons in the visible spectrum
What kind of experiment would confirm electrons have a wave like nature? (1)
Diffraction
Why is it easier to demonstrate wave properties of electrons than of protons? (1)
Easier to accelerate electrons
241/95 Am is produced from decay of 241/94 Pu, state the decay process responsible and explain (2)
Beta minus decay
No change in nucleon number and proton number increases by 1
Explain why a smoke detector using americium-241 emitting alpha radiation poses no risk to the user (2)
Only a small quantity is needed
Alpha emitted only travels a few cm
How it can be told that the weak force is responsible for a decay? (2)
Involves hadrons and leptons
Quark change occurs
Photoelectric emission occurs from a certain metal plate when illuminated by blue but not red light, explain this (4)
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
Outline why wave theory of light fails to explain why blue light causes photoelectric emission and red light does not (2)
Every electron would gain sufficient energy from the waves in time
No matter the frequency of the light
Explain the role of exchange particles (2)
Force carrier
for four fundamental forces
Name two exchange particles that mediate weak force (2)
W boson
Z boson
Explain the process of pair production (2)
Photon interacts with an atom
Energy of photon creates particle antiparticle pair
Explain why pair production cannot take place if the frequency of the photon is below a certain value (3)
Energy of photon depends on frequency
If frequency is below a certain value, there is not enough energy
To provide rest energy of particles
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)
Same energy released in each decay
When beta less than max there is missing energy
Must be another particle to carry away missing energy
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)
Electrons pulled out of gas atoms so gas atoms become positive ions
Conduction due to electrons and positive ions
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)
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
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)
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
