Chp 1, 2, & 3 Particles Flashcards
What’s the relative charge and relative mass of the standard particles
Proton
relative charge — +1
relative mass — 1
Neutron
relative charge — 0
relative mass — 1
Electron
relative charge — -1
relative mass — 0.0005
what’s the symbol for atomic number and nucleon number
atomic number — Z
nucleon number — A
what happens to an unstable nuclei
becomes radioactive
decays over time to diff nuclei to make it more stable
what are radioactive isotopes used for
to find the age by seeing how much carbon-14 is left
because carbon 14 decreases as element decays
what are the diffs and similarities in two isotopes
they have same chemical properties
they have diff physical properties
what are the four 3 acting on the nucleus
Gravitational force — used for attraction
Electrostatic force — used for repulsion
Strong Nuclear Force — used for attraction
what does the strong nuclear force do
- holds nucleus together but the attractive force has to be stronger than the electrostatic force for this to happen
- it has a short range because it holds the nucleons that are a few fm away
- at small separations, the SNF must be repulsive or it would crush the nucleus to a point
when do alpha emissions happen
In Very Big Nucleis
because the nuclei too big for SNF to keep stable
what do the alpha particles emit
4 nucleons
2 protons
how to see alpha particles
using cloud chamber
or
Geiger Counter — bringing it close to alpha source then move it away slowly and observe how the count rate drops
when does Beta decay happen
it happens in neutron rich nucleis
what does beta plus and minus emit in beta decay
Beta minus — takes neutron and converts it to proton and emits an electron and antineutrino
Beta plus — takes a proton and converts it to neutron and emits a positron and a neutrino
how was the neutrino discovered
during beta decay there was energy loss which doesn’t fit in the conservation of energy principle so years later they discovered another particle “antineutrino” which carries energy and momentum away from nuclei
what’s a photon
it’s energy that’s converted into matter and antimatter
what’s pair production
a gamma ray photon is converted into particle- antiparticle pair
what’s annihilation
when particle meets its antiparticle and all the mass is converted into energy
what are the gauge bosons for the diff forces
electromagnetic — virtual photon — for charged particles
weak — W boson — for any particle
Strong — pions — for hadrons only
why does a photon have more range than a W boson
because a W boson has 100x the mass of a virtual. so W boson has a very short range and it also uses a lot of energy so it exists for a short time
meanwhile a photon has almost zero mass so it has infinite range
during weak and strong interaction does strangeness need to be conserved
in strong interaction strangeness MUST BE CONSERVED
in weak interaction strangeness doesn’t have to be conserved
what properties does an antiparticle have
they have the same mass
same rest energy
but opposite charge
what’s the photoelectric effect
it’s the phenomenon used to show that light behaves like a particle
describe the photoelectric effect
when light above a particular frequency is shown on metal, electrons are released and they’re called photoelectrons
what’s the threshold frequency
the minimum frequency of light required for an electron to be emitted
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 photons energy must be greater than the work function in order for the electron to be emitted
if a photon has freq higher than threshold freq 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 the photoelectric effect doesn’t occur what will happen if i increase light intensity
there would be more photons which incident on the metal
however each photon still has the same amount of energy as before
therefore it still doesn’t have enough energy to liberate an electron
so no effect
what’s the photoelectric equation
hf = work function + Ek
what’s the work function
the energy required by an electron to overcome the metallic bond holding it in the metal
how does a fluorescent tube work
high voltage applied across mercury vapour which accelerates fast moving free electrons which collide with mercury atoms
mercury electrons are excited and then return to the ground state, releasing a UV photon
the tubes phosphorous 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 lines appear at discrete points which show where a light photon of specific frequency and wavelength has been absorbed or emitted
what’s wave particle duality
all particles have both particle and wave properties, and wave can have particle properties
what’s the equation for de Broglie wavelength
wavelength = h/mv
a zinc plate with neutral charge is exposed to high freq UV light explain what happens to the charges on plate
the plate becomes positively charged
electrons in metal absorb energy from UV light and leave the surface
