Quantum physics Flashcards
Give two applications of the photoelectric effect
- Night vision goggles
- Digital cameras
What are the steps for the photoelectric effect experiment with E field directed towards the annode?
- Light causes cathode to emit electrons
- E field pushes electrons to annode
- Electrons return to cathode via circuit
- Galvanometer measures current
Draw the diagram for the photoelectric effect experiment
What can we measure if we adjust the pd of the cathode and annode to reverse the E field in the photoelectric effect experiment and adjust its strength to a specific value so that it is pointing towards the cathode?
The maximum kinetic energy of the emitted electrons
What must the voltage between the annode and cathode in the photoelectric experiment be in order for the Kmax to be measured?
VAC = -V0
What is V0?
Stopping potential
Define stopping potential
Voltage required for the most energetic electron released due to light incident on a metalic surface to have zero kinetic energy at the anode
What are the experimental results form the photoelectric effect?
- Photocurrent depends on light frequency
- No mesurable time delay between light being switched on and electrons being released
- Stopping potential depends only on frequency and not intensity of the light
What is einstein’s explination of the photoelectric effect?
Beams of light consist of photons (quanta), the transfer of energy from photon to electron either happens or it doesn’t (photon must have correct energy)
What is the equation for energy of a photon both in terms of frequency and the equation in terms of wave length?
What is the equation for work function of a metal?
What are the three versions of the equation for photon momentum?
*add photo*
Draw the setup of equipment for x-ray production
*add photo*
How are x-rays produced in the x-ray prodution?
- Electrons releaed from cathode by thermionic emission
- Electrons accelerated towards annode by a pd
- When Vac > a few thousand volts, x-rays produced
What is the exact mechanism through which radiation is released near the anode?
Abrupt slowing of electrons due to collisions with the atoms in the annode , this causes a continuous spectrum of x-rays to be emitted
What type of radiation is caused by the rapid deceleration of electrons?
Bremsstrahlung radiation (x-ray)
Give an application for x-rays
To see the interiors of objects opaque to visable light
What is the method for the compton experiment?
- Incident photon hits target electron in carbon target
- Photon scattered at angle theta with greater wavelenght and therefore less energy. Electron is scattered at angle phi
What is the equation that the compton experiment yeilds?
How much energy must a photon have to cause pair prouction?
*add photon*
What is type of photon can cause pair production?
Gamma
Why can’t annihilation produce a single photon?
Both energy and momentum must be conserved
What happens when an electron and a positron meet?
They annihilate eachother producing 2 or 3 photons
Define ‘photomultiplier’
A detector capable of detecting single photons
What happens when we send single photons at a time through a single slit experiment?
We cannot predict where a photon will strike on the screen but over time as we send more photons through a pattern expected for a wave appears
Why can we not treat a photon as a point object?
Because there are fundemental limitaions on the precision which we can simultaneously determine position and momentum of a photon
For a single slit setup if lambda < a (where a is slit width) what is true?
85% of photons go into the central maxima
For a single slit setup what does narrowing the slit do?
Gives a broader diffraction pattern and therfore a greater uncertainty in the y component of momentum of photons moving to outer central maximum
What equation gives the heisenberg uncertainty principal in terms of position?
State the meaning of the heisenberg uncertainty principal
It is impossible to simultaneously determine the position and momentum of a particle with arbritrarily good precision
What is a ‘beat’
A phenomenon where two sound waves of different frequency superimpose over eachother with alternating constructive and destructive interference to give alternating high and low amplitude
What is the heisenberg’s uncertainty equation for energy?
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What is the equation for debrogile wavelength of a particle?
How can the wave nature of electrons be proven?
- Electrons fired at an unbaked nickle surface (as nickle is polycrystaline)
- Electrons give a smooth intensity curve as a function of theta (angle of diffraction)
- When electrons are fired at a ‘baked nickle’ surface (large regions in the atom with alligned crystal planes larger than the electron beam)
- In this case an intensity against angle graph gives a curve instead of a line
Draw the intensity against angle graph for scattering of electrons by ‘baked’ nickle
*add image*
Why do macroscopic objects not diffract? (i.e. humans walking through a doorway)
Debrogile wavelength of macroscopic objects tiny
What limits optical microscopes?
Diffraction effects
What are electron microscopes limited by?
Wavelengths of the electrons
Why are elecron microscopes so much more accurate than optical microscopes?
The electron wavelengths of the electrons used are many thousands of times smaller than those of light
What are two types of electron microscopes?
- Transmission - Electrons pass throught specamin being
- Scanning - Electron beams focused to very fine lines and scanned across the specamin, the beam knocks aditional electrons off the specamin wherever it hits
How is a line spectra produced?
Incoming light has its wavelengths seperated by a prism or diffraction grating
What question in physics did the Rutherford scattering raise?
Why do electrons not fall into the neucleus?
How can an atom emit larger wavelengths of light than it absorbed?
De-exciting through multiple energy levels to get to the ground state
What did Bhor propose to fix the classical modle of the atom?
- Atoms can only exist with specific values of internal energy
- Electrons can only remain excited for short periods of time (~10-8s)
What is the frank-hertz experiment?
An experiment in which electrons pass through mercury vapour in an electric field, this found direct evedence of energy levels
What does each energy level of a hydrogen atom in the Bohr modle represent?
A specigic stable circular orbit of the electron around the neucleus in which it does not radiate any energy
What is equation for the quantized angular momentum of an electron in the Bhor modle of hydrogen?
What type of wave emite no energy?
Standing wave
What equation dictates the orbital radius of an electron in the Bhor modle of hydrogen?
What equation gives orbital speeds of electrons in the Bhor modle of hydrogen?
What is the equtaion for the total energies in the Bohr model?
*add photo*
What is the equation for the Rydberg constant (R)?
Why is there a difference between the mass of a hydrogen atom predicted by the Bhor model and the actual mass?
The Bohr model assumes the neucleus is at rest but in reality it is not and this decreases the mass
Define a hydrogen like atom
A neucleus orbited by a single electron
Does quantum mechanics view things as waves or particles?
Waves
Define ‘free particle’
A particle that experiences no forces as it moves along the x-axis
What does Psi(x,t) mean?
It gives the distribution of a particle in space
How do we find the probaility of a wave being at a certain point?
Square the absolute value of Psi(x,t) at a point
