Quantum Flashcards
Why is the strong force both attractive and repulsive?
To prevent the nucleus from collapsing or exploding
When is the strong force attractive?
> 0.5 fm
When is the strong force repulsive?
< 0.5 fm
What is the force responsible for beta decay?
the weak force
How strong is the weak force? (relative)
1 millionth of the strong force
How does the range of the weak force compare to that of the strong force?
It has a smaller range
What does the weak force act on?
Leptons and hadrons
What are the types of beta decay?
β+ and β-
When does beta decay occur?
When the nucleus emits an electron or a positron
What does a free neutron decay into in beta decay?
A proton, an electron and an anti-neutrino
What does a free proton decay into in beta plus decay?
A neutron, a positron and a neutrino
What type of beta decay is it when a free neutron decays into a proton?
β-
What type of beta decay is it when a free proton decays into a neutron?
β+
Why it called β- decay when a neutron decays into a proton?
An electron is produced
Why is it called β+ decay when a proton decays into a neutron?
A positron is produced
What happens to the unaccounted-for energy in beta decay?
It is carried away by the neutrinos
What happens if the nucleus is still unstable after emitting alpha or beta radiation?
It is in an excited state, and gives off gamma radiation
What does the strong force overcome?
The electrostatic forces of repulsion between protons in the nucleus
What type of particle are neutrinos?
Leptons
When are electromagnetic waves emitted?
When a charged particle loses energy
In what form is electromagnetic radiation emitted?
Photons - bursts or packets of energy
How do photons travel?
In one direction only in a straight line
What is one electron volt defined as?
The energy transferred when an electron is moved through a p.d. of 1V
What will happen if a particle-antiparticle pair meet?
They will annhiliate each other, their mass is converted into two gamma ray photons
What is pair production?
When a photon (γ) with enough energy can change into a particle antiparticle pair
What particles does the strong interaction affect?
Hadrons
Define ionisation energy
The energy required to remove an electron from an atom’s ground state
Define excitation energy
The energy required to raise an electron from ground state to an excited state
Define quantisation of energy levels
Energy levels take discrete/specific values of energy
What are 2 ways to excite an atom?
Collision of free electron:
(colliding electron transfers KE to atom’s electrons -> atomic electron moves to higher shell)
Absorption of photon:
(incoming photon transfers E to atomic electron, BUT photon must have EXACT amount of energy to cause excitation)
What happens when an excited electron de-excites?
A photon is emitted, equal to the change in E
What is the difference between excitation and ionisation?
EXCITATION: electron goes up energy level, falls back down, photon is emitted
IONISATION: electron leaves atom, results in free electron + free atom
The gold leaf electroscope is used to detect ______. When the stem and leaf become charged, the gold leaf is _________ by the stem and ________.
When the charge leaves the system so that the charge of the gold leaf and stem are _______, the gold leaf _____.
charge / repelled / rises / neutral / falls
What happens in an atom when line spectra are produced?
When electrons in atoms are excited, a photon of a specific energy is emitted, which can be seen as different colours on the line spectra
Why is the line spectrum of an element unique to that element and can be used to identify it?
Energy levels for each atom are unique, so photons produced for each atom are different.
Each element produces a unique set of spectral lines to identify them
Why are there dark lines on the absorption spectrum?
-Dark lines correspond to the [photons missing from the continuous spectrum of PARTICULAR WAVELENGTHS
-these photons excite electrons in the gas because they have the EXACT energy equal to the energy levels in the atom
- E = hc/λ
Why do interference patterns only occur sometimes?
How to get absorption spectra
-shine lots of white light through cool gas
-only certain photons (colours) absorbed
-we see a black line where no night gets through
How to get emission spectra
-shine light through a diffraction grating
-splits up the colours to show certain frequencies of light
