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Theoretical physics year 1 > Quantum physics > Flashcards

Quantum physics Flashcards

1
Q

Give two applications of the photoelectric effect

A
  • Night vision goggles
  • Digital cameras
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2
Q

What are the steps for the photoelectric effect experiment with E field directed towards the annode?

A
  • Light causes cathode to emit electrons
  • E field pushes electrons to annode
  • Electrons return to cathode via circuit
  • Galvanometer measures current
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3
Q

Draw the diagram for the photoelectric effect experiment

A
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4
Q

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?

A

The maximum kinetic energy of the emitted electrons

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5
Q

What must the voltage between the annode and cathode in the photoelectric experiment be in order for the Kmax to be measured?

A

VAC = -V0

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6
Q

What is V0?

A

Stopping potential

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7
Q

Define stopping potential

A

Voltage required for the most energetic electron released due to light incident on a metalic surface to have zero kinetic energy at the anode

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8
Q

What are the experimental results form the photoelectric effect?

A
  • 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
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9
Q

What is einstein’s explination of the photoelectric effect?

A

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)

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10
Q

What is the equation for energy of a photon both in terms of frequency and the equation in terms of wave length?

A
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11
Q

What is the equation for work function of a metal?

A
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12
Q

What are the three versions of the equation for photon momentum?

A

*add photo*

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13
Q

Draw the setup of equipment for x-ray production

A

*add photo*

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14
Q

How are x-rays produced in the x-ray prodution?

A
  1. Electrons releaed from cathode by thermionic emission
  2. Electrons accelerated towards annode by a pd
  3. When Vac > a few thousand volts, x-rays produced
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15
Q

What is the exact mechanism through which radiation is released near the anode?

A

Abrupt slowing of electrons due to collisions with the atoms in the annode , this causes a continuous spectrum of x-rays to be emitted

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16
Q

What type of radiation is caused by the rapid deceleration of electrons?

A

Bremsstrahlung radiation (x-ray)

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17
Q

Give an application for x-rays

A

To see the interiors of objects opaque to visable light

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18
Q

What is the method for the compton experiment?

A
  1. Incident photon hits target electron in carbon target
  2. Photon scattered at angle theta with greater wavelenght and therefore less energy. Electron is scattered at angle phi
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19
Q

What is the equation that the compton experiment yeilds?

A
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20
Q

How much energy must a photon have to cause pair prouction?

A

*add photon*

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21
Q

What is type of photon can cause pair production?

A

Gamma

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22
Q

Why can’t annihilation produce a single photon?

A

Both energy and momentum must be conserved

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23
Q

What happens when an electron and a positron meet?

A

They annihilate eachother producing 2 or 3 photons

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24
Q

Define ‘photomultiplier’

A

A detector capable of detecting single photons

25
Q

What happens when we send single photons at a time through a single slit experiment?

A

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

26
Q

Why can we not treat a photon as a point object?

A

Because there are fundemental limitaions on the precision which we can simultaneously determine position and momentum of a photon

27
Q

For a single slit setup if lambda < a (where a is slit width) what is true?

A

85% of photons go into the central maxima

28
Q

For a single slit setup what does narrowing the slit do?

A

Gives a broader diffraction pattern and therfore a greater uncertainty in the y component of momentum of photons moving to outer central maximum

29
Q

What equation gives the heisenberg uncertainty principal in terms of position?

A
30
Q

State the meaning of the heisenberg uncertainty principal

A

It is impossible to simultaneously determine the position and momentum of a particle with arbritrarily good precision

31
Q

What is a ‘beat’

A

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

32
Q

What is the heisenberg’s uncertainty equation for energy?

A

*add photo*

33
Q

What is the equation for debrogile wavelength of a particle?

A
34
Q

How can the wave nature of electrons be proven?

A
  • 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
35
Q

Draw the intensity against angle graph for scattering of electrons by ‘baked’ nickle

A

*add image*

36
Q

Why do macroscopic objects not diffract? (i.e. humans walking through a doorway)

A

Debrogile wavelength of macroscopic objects tiny

37
Q

What limits optical microscopes?

A

Diffraction effects

38
Q

What are electron microscopes limited by?

A

Wavelengths of the electrons

39
Q

Why are elecron microscopes so much more accurate than optical microscopes?

A

The electron wavelengths of the electrons used are many thousands of times smaller than those of light

40
Q

What are two types of electron microscopes?

A
  • 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
41
Q

How is a line spectra produced?

A

Incoming light has its wavelengths seperated by a prism or diffraction grating

42
Q

What question in physics did the Rutherford scattering raise?

A

Why do electrons not fall into the neucleus?

43
Q

How can an atom emit larger wavelengths of light than it absorbed?

A

De-exciting through multiple energy levels to get to the ground state

44
Q

What did Bhor propose to fix the classical modle of the atom?

A
  • Atoms can only exist with specific values of internal energy
  • Electrons can only remain excited for short periods of time (~10-8s)
45
Q

What is the frank-hertz experiment?

A

An experiment in which electrons pass through mercury vapour in an electric field, this found direct evedence of energy levels

46
Q

What does each energy level of a hydrogen atom in the Bohr modle represent?

A

A specigic stable circular orbit of the electron around the neucleus in which it does not radiate any energy

47
Q

What is equation for the quantized angular momentum of an electron in the Bhor modle of hydrogen?

A
48
Q

What type of wave emite no energy?

A

Standing wave

49
Q

What equation dictates the orbital radius of an electron in the Bhor modle of hydrogen?

A
50
Q

What equation gives orbital speeds of electrons in the Bhor modle of hydrogen?

A
51
Q

What is the equtaion for the total energies in the Bohr model?

A

*add photo*

52
Q

What is the equation for the Rydberg constant (R)?

A
53
Q

Why is there a difference between the mass of a hydrogen atom predicted by the Bhor model and the actual mass?

A

The Bohr model assumes the neucleus is at rest but in reality it is not and this decreases the mass

54
Q

Define a hydrogen like atom

A

A neucleus orbited by a single electron

55
Q

Does quantum mechanics view things as waves or particles?

A

Waves

56
Q

Define ‘free particle’

A

A particle that experiences no forces as it moves along the x-axis

57
Q

What does Psi(x,t) mean?

A

It gives the distribution of a particle in space

58
Q

How do we find the probaility of a wave being at a certain point?

A

Square the absolute value of Psi(x,t) at a point

59
Q
A

Theoretical physics year 1 (3 decks)

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