Particles

Are electromagnetic waves transverse or longitudinal?

Transverse.

What are the differences between the constitutents of a nuclide after it undergoes electron capture

It has 1 more neutron

1 less proton

Electron neutrino emission

The combination of the proton and electron also produces an electron neutrino

p+e −→n+ν e

Radiation types

Alpha:

highest ionising

range in air 5cm

stopped by paper

Beta:

high ionising

range in air1m

stopped by a few mm of aluminium.

Gamma:

low ionising

range a few KM

stopped by several cm of thick lead

Diffraction and momentum relationship

The amount of diffraction (the spread of the particle's wave-like behavior) increases as the momentum of the particle decreases (since wavelength is inversely related to momentum).

Separation of maxima in the diffraction pattern

The separation of the maxima in the diffraction pattern depends on the wavelength. The wavelength of a particle is inversely proportional to its momentum. This means that bu changing the velocity the momentum and wavelength can be altered.

And finally, the velocity can be altered by changing the voltage.

How are electrons detected in a cloud chamber

Particles are detected in a cloud chamber by leaving a visible trail as they ionize the surrounding gas molecules

The lower the refractive index of a light?

The greater the critical angle

If the energy incident per second is kept the same what happens to the amount of electrons being emitted from the metal if there is also more energy per photon?

Fewer photons so fewer electrons are emitted, but they have more KE

Only transverse waves can be …

Polarised

Electron capture

A process where an electron is captured by a proton in the nucleus, forming a neutron and emitting a neutrino.

What phenomenon can be used to show that light behaves as a particle?

The photoelectric effect.

Describe the photoelectric effect.

When light above a particular frequency is shone on metal, electrons are released - these released electrons are “photoelectrons”.

What is the threshold frequency?

The minimum frequency of light required for an electron to be emitted.

What equation is used to determine the energy of a photon?

E = hf = hc/𝜆

Energy = Planck’s constant x frequency

Energy = (PC x 3 x 10^8) / wavelength

Why does a photon need to have a minimum frequency in order to liberate an electron?

The energy of the photon is determined by its frequency, the photon’s energy must be greater than the work function (energy needed to break bonds holding the electron) in order for an electron to be emitted.

If a photon has a frequency higher than the threshold frequency, what would occur?

The electron will be liberated and the remaining energy is the kinetic energy of the electron.

If light is incident on a metal and photoelectric emission does NOT occur, what is the effect of increasing light intensity?

● If it is more intense then there would be more photons incident on the metal each second

● However each photon still carries the same amount of energy as before

● Therefore it still does not contain enough energy to liberate an electron

● No effect

Define the work function.

The energy required by an electron to overcome the metallic bond holding it in the metal.

What is an electron volt?

The kinetic energy of an electron that has been accelerated from rest through a potential difference of 1V.

How does a fluorescent tube work?

● High voltage applied across mercury vapour accelerates fast

moving free electrons which collide with the mercury atoms.

● Mercury electrons are excited and then return to the ground state, releasing a UV photon.

● The tube’s phosphorus coating absorbs the UV photons and its electrons are excited, they cascade down the energy levels and emit visible light photons.

What can be used as evidence for the discrete energy levels in atoms?

Line emission and absorption spectra as the lines appear at discrete points which show where a light photon of specific frequency and wavelength has been absorbed or emitted, this shows electrons can only absorb an exact amount of energy to be excited to the next discrete energy level.

What is wave particle duality?

All particles have both particle and wave properties, waves can have particle properties e.g. light acts as a particle in the photoelectric effect and as a wave when it is diffracted.

What is the equation for de Broglie wavelength?

𝝺 = h / mv

Where mv is momentum.

What are the main constituents of an atom?

● Proton

● Neutron

● Electron

What is meant by specific charge?

The charge to mass ratio: Specific charge = charge / mass Units C/kg.

What is the specific charge of a proton?

Protons have charge +1.6 x 10^-19 and mass

1.67 x 10^-27 kg

Specific charge = 1.6 x 10^-19/1.67 x 10^-27

= 9.58 x 10^7 C/kg

What is the letter associated with a proton number?

Z

What is a nucleon?

A constituent of the nucleus: a proton or a neutron.

What letter represents nucleon number?

A.

What is an isotope?

A version of an element with the same number of protons but a different number of neutrons.

State a use of radioactive isotopes.

Carbon dating - the proportion of carbon-14 in a material can be used to estimate its age.

What is the strong nuclear force?

The fundamental force that keeps the nucleus stable by counteracting the electrostatic force of repulsion between protons.

Describe the range of the strong force?

● Repulsive up to 0.5 fm

● Attractive from 0.5-3 fm

● Negligible past 3 fm

What makes a nucleus unstable?

Nuclei which have too many of either protons or neutrons or both.

How do nuclei with too many nucleons decay?

Alpha decay (emission of a helium nucleus formed of 2 protons and 2 neutrons).

How do nuclei with too many neutrons decay?

Beta minus decay in which a neutron decays to a proton by the weak interaction (quark character has changed from udd to uud).

How was the existence of the neutrino

hypothesised?

The energy of particles after beta decay was lower than before, a particle with 0 charge (to conserve charge) and negligible mass must carry away this excess energy, this particle is the neutrino.

What is meant by beta minus decay?

When a neutron turns into a proton, the atom releases an electron and an anti-electron neutrino.

What is an alpha particle?

A particle contains two protons and two neutrons, the same as a helium nucleus

What is an antiparticle?

For each particle there is an antiparticle with the same rest energy and mass but all other properties are the opposite of its respective particle.

True or false: ‘Every particle has a antiparticle’

True.

What is the name of the antiparticle of an electron?

Positron

What is the antiparticle of π0 (pion with 0 charge)?

π0, its antiparticle is itself.

What occurs when a particle and antiparticle meet?

Annihilation:

The mass of the particle and antiparticle is converted back to energy in the form of 2 gamma ray photons which go in opposite directions to conserve momentum.

What is pair production?

A gamma ray photon is converted into a particle-antiparticle pair.

Name the 4 fundamental forces?

● Gravity

● Electromagnetic

● Weak nuclear

● Strong nuclear

The virtual photon is the exchange particle of which force?

The electromagnetic force.

What type of particles are affected by the strong nuclear force?

Hadrons.

What is the exchange particle of the

weak nuclear force?

The W boson (W+ or W-).

What does the electromagnetic force act on?

It acts on charged objects, for example when a positively charged ball repels another positively charged ball.

When does weak nuclear interaction occur?

When quark character changes (a quark changes into another quark), it affects all types of particles.

Which properties must be conserved in particle interactions?

● Energy

● Charge

● Baryon number

● Lepton number

● Momentum

● Strangeness (only for strong interactions)

What is a hadron?

Both baryons and mesons are hadrons, hadrons are made of 2 or more quarks held together by the strong nuclear force.

What are the classes of hadrons?

● Baryons (three quarks)

● Mesons (1 quark, 1 antiquark)

The pion and kaon are both examples of which class of particle?

Mesons.

The pion can be an exchange particle for which force?

The strong nuclear force.

What particle does a kaon decay into?

A kaon decays into a pion.

Give some examples of baryons?

● Proton - uud

● Neutron - ddu

What is significant about a proton?

● It is the only stable baryon

● All baryons will eventually decay into protons

What are some example of leptons?

● Electron

● Muon

● Neutrino

● (the antiparticles of the above)

What does a muon decay into?

An electron and two types of neutrino.

What is the strangeness value of a strange quark?

-1

True or false: ‘Strangeness is always conserved in a weak interaction’

False.

Strangeness is only conserved in the strong interaction, in weak interactions it can change by 0, -1 and +1.

Complete the sentence:

Strange particles are produced through the _____________ and decay through the ____________.

Strange particles as particles that are produced through the strong interaction and decay through the weak interaction.

Charge

Always indicated by the particle.

Baryon number

0 except for baryons which are +1

L_μ

0 except for a muon and muon neutrino which are +1

L_e

0 except for an electron and electron neutrino which are +1

photocell

A photocell also shows the photoelectric effect. UV radiation is incident on the negatively charged plate which allows electrons to flow to the positive cathode.

Excitation

Is the movement of electrons up to a higher energy level; either an electron collides with the orbital electron or a photon is absorbed by it, transferring energy to it. When the electron de-excites, it moves down in energy levels and emits a photon.

Ionisation

Is when an electron is removed from an atom

Alpha Decay

The process of an unstable nucleus emitting an alpha particle (two protons and two neutrons) to become more stable.

Annihilation

The process of a particle and its antiparticle colliding and being converted into energy. The energy is released in two photons to conserve momentum.

Antiparticle

All particles have a corresponding antiparticle with the same mass but opposite charge and conservation numbers.

Baryon Number

A quantum number that is conserved in all particle interactions. Baryons have a baryon number of +1 and non-baryons have a baryon number of 0.

Baryon

A class of hadron, that is made up of three quarks. The proton is the only stable baryon.

Beta-Minus Decay

The process of a neutron inside a nucleus turning into a proton, and emitting a beta-minus particle (an electron) and a antineutrino.

Beta-Plus Decay

The process of a proton inside a nucleus turning into a neutron, and emitting a beta-plus particle (a positron) and a neutrino.

Electron Diffraction

The spreading of electrons as they pass through a gap similar to the magnitude of their de Broglie wavelength. It is evidence of the wave-like properties of particles.

Electron-volt (eV)

The work done to accelerate an electron through a potential difference of 1 V. 1 eV is equal to the charge of an electron (E = qv).

Energy Levels

Defined and distinct energies at which electrons can exist in an atom. An electron cannot exist between energy levels.

Excitation

The process of an electron taking in exactly the right quantity of energy to move to a higher energy level.

Gauge Boson

The exchange particles that transmit the four fundamental interactions between particles.

Ground State

The most stable energy level that an electron can exist in.

Hadrons

A class of subatomic particle that experiences the strong nuclear interaction.

Ionisation

The process of an atom losing an orbital electron and becoming charged.

Isotope

Same number of protons but different numbers of neutrons.

Isotopic Data

Data from isotopes that can be used for a purpose, such as carbon dating.

Kaon

A type of meson that decays into pions.

Lepton Number

A quantum number that is conserved in all particle interactions. Both electron lepton numbers and muon lepton numbers must be conserved.

Lepton

A group of elementary subatomic particles, consisting of electrons, muons and neutrinos.

Meson

A class of hadron that is made up of a quark and antiquark pair.

Muon

A type of lepton that decays into electrons.

Neutrino

A subatomic particle whose existence was hypothesised to maintain the conservation of energy in beta decay.

Nucleon Number (A)

The sum of the number of protons and neutrons in a given nucleus.

Nucleon

A proton or neutron.

Pair Production

The process of a sufficiently high-energy photon converting into a particle and its corresponding antiparticle. To conserve momentum, this usually occurs near a nucleus.