Physics - Particles

In what two ways can light behave?

It can behave as a particle in the photoelectric effect and as a wave as diffraction happens on a narrow gap

What is an electronvolt?

The energy gained by a 1C charge when it is accelerated through a potential difference of 1V

In what two ways can particles behave?

They behave as waves in diffraction when they cause a interference pattern and as a particle as they deflect when travelling through a magnetic field.

How is an absorption spectra formed?

White light is passed through a cool gas where photons with the same energy as the energy gaps between the atoms are absorbed. They are passed through a prism where black lines are produced on the spectrum. They represent the wavelengths for the energy transitions for the electrons in the atom.

How are line emission spectra formed?

An electric current is passed through a sample of gas. Electrons collide with orbital electrons in the gas atoms which transfers energy and excites the atoms. Orbital electrons de excite and emit photons of particular f and wavelengths. The gas emits these photons which get produced on a line emission spectrum.

Why do photons of particular frequencies cause excitations?

Electrons occupy discrete energy levels so need an exact amount of energy to excite (the work function). All of a photons energy is absorbed due to the 1 to 1 interaction between electrons and a photon. As E=hf, photons need a specific frequency to provide this energy (the threshold frequency). The energy levels of atoms of an element will be the same so the energy change between the levels will be the same.

What does it mean when an electron is in its ground state?

The electrons in the atom are in their lowest energy state.

Conservation of strangeness rule?

Strangeness is not conserved in the weak interaction when kaons decay

Strangeness is conserved in the strong interaction when kaons are formed

How was the neutrino discovered?

It accounted for the conservation of energy in beta decay

What does wave particle duality suggest?

Electron diffraction suggests that particles possess wave properties, and the photoelectric effect suggests that waves have a particulate nature.

Equation for specific charge?

Charge/Mass

Give the properties of the strong nuclear force.

It acts between nucleons only. It is attractive up to 3fm but repulsive at a range below 0.5fm.

Equation for pair production and annihilation?

E=hf

What is pair production?

When a photon is converted into equal amounts of matter and antimatter. This can only occur if the photon has energy greater than the total rest energy of the created particles, the excess energy is converted to Ek

What is annihilation?

When a particle and its antiparticle collide, where their rest energies and Ek at time of impact is converted to energy which is released in the form of 2 gamma ray photons in oppoosite directions so that momentum can be conserved.

What feels the strong force and what is the exchange particle?

Hadrons, gluon

What feels the weak force and what is the exchange particle?

all particles, W boson

What feels the electromagnetic force and what is the exchange particle?

Charged Particles, photon

What feels the force of gravity?

Any particle with mass

What is the threshold frequency?

The minimum frequency of light needed to be shone on a metal so that photoelectrons are emitted from it.

What is the work function?

The minimum energy needed for electrons to be emitted from the surface of the metal.

What is the stopping potential?

The potential difference needed across the metal to stop the photons with the maximum kinetic energy.

What is the equation for stopping potential?

Ek max = eV

What is conserved in interactions?

Lepton Number, Baryon Number, charge (and strangeness only if kaons are formed)

What attractive forces act between nucleons?

Strong nuclear force, gravitational force is negligible

What repulsive force acts between nucleons? 

Electromagnetic force

What is the equation for electron capture?

proton + electron → neutron + electron neutrino

What is a particle called when it doesnt fit in the standard model?

Composite

What do all baryons decay into?

Protons

What do kaons decay into and through what interaction?

Pions through the weak interaction

What do muons decay into?

electrons

What force is responsible for beta decay?

Weak force

In the weak interaction, what does strangeness change by?

0, +1 or -1

For a graph of energy against frequency, what is the y intercept?

the work function of the metal

For a graph of energy against frequency, what is the x intercept?

the threshold frequency

What does it mean when an electron becomes excited?

It absorbs an exact amount of energy to move up to a higher energy level

What is the photoelectric effect?

The phenomena when photoelectrons are emitted from the surface of a metal when light above a certain frequency is shone on it.

When are photons emitted?

when electrons move down energy levels

What does increasing intensity/power in the photoelectric effect do?

Increases number of photons emitted per second from the source

In the fluorescent tube, what type of light does the phosphorus coating emit?

Visible

In the fluorescent tube, what type of light does the mercury vapour emit?

UV

Why do leptons and a proton not decay further when produced?

They are all stable and the proton is the only stable baryon.

Which particle is used in a nuclear reactor to turn stable atoms into radioactive ones? Why?

Neutrons as they are not products of radioactive decay and can pass into the nucleus without being repelled away.