Particles and radiation Flashcards
UV light is shone on a zinc plate and the number of photoelectrons counted. What happens to the number of electrons counted if:
a) two lamps are used?
b) a sheet of glass is placed between the UV lamp and the metal plate?
c) the lamp is moved twice as far away?
a) brightness doubles, twice as many electrons emitted per second
b) Glass blocks UV Light, no electrons emitted
c) 4x less light hits the metal plate due to inverse square law, 4x fewer electrons emitted per second
In the photoelectric effect, does light behave as waves or particles
Particles
Describe method of gold leaf experiment
- rub plastic rod with cloth to transfer electrons from cloth to the rod, leaving plastic rod with negative charge
- By touching rod to the zinc plate, electrons transfer from rod to the plate leaving the plate with a negative charge.
- The negative charge flows down the metal stem and into the stem and gold leaf.
- Because the stem and gold leaf are both negatively charged they repel each other and the gold leaf rises.
Describe what happens if a beam of blue light shone onto zinc plate in gold leaf experiment
- electrons liberated from surface
- plate, metal stem and gold leaf lose their charge
- gold leaf and metal stem no longer repel each other and the leaf falls
In normal gold leaf experiment, rod and cloth rub together and rod becomes negatively charged
This time a glass rod is rubbed with a cloth causing it to become positively charged. This glass rod is brought into contact with the metal plate causing the system to become positively charged.
a) Will the gold leaf still rise and if so why?
b) A UV lamp (above the threshold frequency) is shone onto the metal plate. State and explain whether the gold leaf will fall and why.
Yes, it will still rise
Stem and leaf become positively charged
So they still repel each other
b) Gold leaf will not fall
Electrons are emitted from metal plate
Stem and leaf will become more positively charged
Leaf could rise even further
Define the electron volt (eV)
The kinetic energy gained by 1 electron passing through a potential difference of 1 volt
What is stopping potential
Voltage of the battery when the current is zero
How do you get a circuit to stopping potential
Equation for stopping potential
Ek max = eVs
- where lowercase e is the charge of electron
Re arrange to get Vs= Ekmax/ e
When does fluorescence occur
When UV light is absorbed by a material which then emits UV light
Why is a fluorescent tube filled with mercury vapour at a low pressure
Incident electrons need to pass through tube
So can’t be too many collisions per second with the mercury
Or a current can’t be sustained
In fluorescent tube, mercury atoms produce UV light, how to convert protons to visible wavelengths
Add a phosphor coating to the tube, phosphor atoms absorb UV and re emit visible light
Explain point of coating inside fluorescence tube
Phosphor coating absorbs UV emitted by mercury
This excites orbital elections in phosphor
When orbital electrons de-excite they emit visible photons
Because energy levels closer together
Describe electron diffraction experiment
Electrons fired from hot filament & accelerated towards graphite.
Electrons have de broglie wavelength similar to size of spacing of carbon atoms passing through.
Electrons diffract and spread out showing diffraction
Bright ring of constructive interference and dark rings of destructive interference produced at end of tube
Equation for beta minus decay
Define an antiparticle
A particle that has the same mass but opposite charge corresponding to their opposing particle
What happens in annihilation, use electron and positron as an example
They collide and annihilate and produce two high energy photons
- two photons needed to follow law of conservation of momentum, must be travelling in opposite directions
- You must also say that they are a pair of gamma rays
What is pair production
A photon of high energy of EM radiation creates to exist creating a particle and an associated antiparticle
Higgs boson is the heaviest particle of the standard model. Why did it take so long to create the Higgs boson which was created in 2012
Particle collisions didn’t have an energy equal to or greater than Higgs boson rest energy
The formula booklet says Beta ^- particle should have a kinetic energy equal to 0.6MeV. However this is not the case as no Beta ^- particle has this much KE. Where does the rest go
The antineutrino which was really hard to detect
What does the strong force act on and what is it’s ranges
Acts on all hadrons and quarks
Range : 0 - 0.5fm, repulsive 0.5fm - 3fm, attractive
What is the Higgs boson
It creates a field that gives mass to particles
What is the strangeness for all Kaons
K^+ & K^0 have S=+1
K^- have S=-1