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Physics A Level Better One > Quantum > Flashcards

Quantum Flashcards

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1
Q

What is the Photoelectric Affect?

A

The process of removing an electron from the surface of a metal due to light incident on its surface

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2
Q

What is the Photoelectric Equation?

A

hf = Φ + Ek

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3
Q

What is Threshold Frequency?

A

The minimum frequency required to emit electrons from the surface of a metal

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4
Q

What is Work Function?

A

The minimum energy required to remove an electron from the surface of a metal

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5
Q

What is Ionization?

A

When an atom either gains or loses an electron, giving a charge

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6
Q

What is Excitation?

A

Where an atom absorbs energy, causing an electron to move to a higher energy level with ionisation

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7
Q

What happens in De-Excitation?

A

An electron moves from a higher energy state to a lower energy state and emits a photon in the process

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8
Q

What is the Emitted Photon Equation?

A

hf = E1 - E2

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9
Q

What is the De Broglie Equation?

A

λ = h / mv

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10
Q

What is the conversion for eV to J?

A

1eV = 1.6x10^-19J

-Charge of an electron

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11
Q

Why don’t free electrons escape the metal?

A

Still electrostatically attracted to the positive ions so stay in the metal. Don’t have the energy to overcome the attraction

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12
Q

Why do electrons escape with a range of Ek?

A

Because some are deeper in the surface of the metal and have to do more work to escape

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13
Q

In a graph showing Ek max against frequency, what is the gradient?

A

Planck Constant

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14
Q

In a graph showing Ek max against frequency, what is the x intercept?

A

f₀

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15
Q

In a graph showing Ek max against frequency, what is the y intercept?

A

-Φ

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16
Q

What components are in a vacuum photo cell circuit?

A

Photoemissive electrode, wire, microammeter, variable DC supply

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17
Q

What is a Vacuum?

A

No particles

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18
Q

When the photons enter the vacuum photo cell what leaves the photoemissive electrode and what does this create?

A

Electrons, a current

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19
Q

If we increase frequency in a vacuum photocell circuit what happens to current, why?

A

No change, same number of electrons crossing gap per second (they just have more Ek(max))

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20
Q

If we increase intensity in a vacuum photocell circuit what happens to current, why?

A

Current increases, more photons arrive per second, more e-s per second cross the gap, same Ek(max) as before

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21
Q

What is Stopping Potential?

A

The minimum p.d. required to stop all of the e-s crossing the gap (even ones at Ek(max)), the current becomes 0

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22
Q

What happens to current as p.d increases

A

Decreases

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23
Q

What can happen when an orbiting electron gains energy?

A

It can be promoted to a higher energy level

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24
Q

When an electron is promoted to a higher energy level what do we call it?

A

Excited

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25
Q

How does an electron gain energy to get excited?

A

Collision with a passing electron or absorbing a photon of EM radiation

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26
Q

What do we call an electron when it’s in it’s normal energy level?

A

Ground state

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27
Q

What will the energies needed to promote an e- to a higher energy level be measured in?

A

eV

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28
Q

Does an e- have to return directly to the ground state?

A

No

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29
Q

What does the excited e- emit when it returns to the ground state?

A

A photon of energy

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30
Q

A photon that is emitting by an e- going directly to a ground state has what?

A

Highest energy and highest frequency

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31
Q

A photon that is emitted by an e- relaxing from a higher energy level to a lower energy level but not returning directly to the ground state has what?

A

Lower energy, longer wavelength

32
Q

How do you calculate the length of the wavelength of a photon emitted by an excited e- relaxing?

A

Convert eV into J, use E = hc/λ, rearrange to find λ

33
Q

What is the equation that connects E, h and f?

A

E = hf

34
Q

What is the equation that connects E, h, c and λ?

A

E = hc/λ

35
Q

What is the equation that connects h, f, E1 and E2

A

hf = E1 - E2

36
Q

What do we call it when an excited e- returns to ground state?

A

De-exciting or relaxing

37
Q

Each element has a specific set of?

A

Discrete energy levels

38
Q

Define discrete

A

Separate, not continuous data

39
Q

When an electron de-excites and releases a photon the photon can only have what? What is this equal to?

A

Certain energy values, equal to the difference in energy levels

40
Q

The frequency and wavelength are dependant on the ______?

A

Photon energy

41
Q

What is the visible light range?

A

400nm to 700nm

42
Q

How do you set up an absorption spectra?

A

Shoot white light through a cloud of gas and observe with a telescope

43
Q

As white light passes through a gas why do certain photons get absorbed?

A

Because their energies match possible gaps in the atom’s energy levels

44
Q

On absorption spectra what do the missing photons show up as?

A

Dark lines

45
Q

What is an ion?

A

A charged atom

46
Q

Define ionisation energy

A

The minimum energy required to remove an electron in the ground state from an atom

47
Q

What are the three things inside a fluorescent tube?

A

Low pressure mercury gas atoms, free electrons, powder coating

48
Q

Why do we apply a high p.d to a fluorescent tube

A

To remove electrons from some of the gas atoms, turning them into positive ions

49
Q

What do the positive ions do in the fluorescent tube

A

Accelerate towards the negative electrode and dislodge electrons from the electrode

50
Q

What do the free electrons in a fluorescent tube do?

A

Accelerate towards the positive electrode and collide with mercury atoms along the way, exciting them

51
Q

When a mercury atom gets excited it releases a what, of which type?

A

A high energy UV photon

52
Q

What absorbs the UV from the mercury atom and what happens?

A

The powder coating around the tube, it excites

53
Q

What happens when the powder coating excites?

A

The atom de-excites through smaller intermediate energy levels, releasing lower frequency photons (visible light)

54
Q

Why is there high pressure and high p.d in a fluorescent tube?

A

Ensures the e-s ca reach the required speeds (by accelerating between collisions) to excite the mercury atoms

55
Q

Why do we need a powder coating in a fluorescent tube, why can’t we just have mercury?

A

Because mercury emits photons with too high a frequency to see and it wouldn’t make light

56
Q

EM radiation can behave as what two things?

A

Wave or particle

57
Q

What are the qualities of EM radiation that suggest it’s a wave? (5)

A

Reflection, refraction, diffraction, interference, polarisation

58
Q

What are the qualities of EM radiation that suggest it’s a particle?

A

The photelectric affect

59
Q

What is the de Broglie hypothesis?

A

A particle, mass m, moving with speed v, has an associated wavelength, λ, the ‘de Broglie wavelength

60
Q

What is the equation for the de Broglie wavelength?

A

λ = h/p = h/mv

61
Q

How has the de Broglie wavelength been proved?

A

By electron diffraction experiments

62
Q

What is diffraction?

A

Where the edges of a wave spread out when it passes an obstacle or through a gap

63
Q

If λ is equal to gap size what is the diffraction?

A

Strong

64
Q

If λ > gap size what is the diffraction?

A

It reflects and doesn’t pass through

65
Q

If λ < gap size what is the diffraction?

A

Weak

66
Q

When asked the minimum p.d for an e- to be accelerated through for ionisation how do we answer?

A

For ionisation to occur it must supply difference from ionisation level and ground state, put this value into eV, e- is accelerated through eV value in just V

67
Q

How do we answer questions asking about doubling light intensity? What assumptions are made?

A

x2 photons, x2 e-s, current = rate of flow of charge, x2 current. Ek max stays constant and unchanged. Assume 1 photon removes 1 e-, assume all photoelectrons are collected

68
Q

What shows e-s are particles?

A

Deflection in EM fields

69
Q

Why does the gold leaf fall when radiation is absorbed into electroscope?

A

Energy of rad > Φ so photoelectrons are emitted and the electroscope discharges (becauses e-s and their - charge is leaving), leaf and metal stem no longer repel and the leaf falls

70
Q

Why won’t only visible light being absorbed (for zinc) let the gold leaf fall?

A

VL f < UV f, or VL E < Φ, so leaf doesn’t fall becuase no e-s are escaping so everything is still charged and repelling

71
Q

When plate is given + charge why doesn’t gold leaf fall?

A

Higher voltage, harder for e-s to leave, gold leaf doesn’t fall

72
Q

What does an e- have to pass through to diffract?

A

The gap between two nuclei

73
Q

Roughly how big is the atomic diameter?

A

10^-10m

74
Q

Why does there being no time delay for the photoelectric effect prove light is a particle?

A

Light travels as photons, transfers E in discrete packets in 1 to 1 interactions

75
Q

Why does Ek have a max value?

A

hf is energy available/ always the same energy from the photons, energy required varies (some e-s deeper) so Ek varies

76
Q

Why only certain values of f cause excitation

A

e-s occupy DISCRETE energy levels, need to absorb exact energy levels to move to a higher level, photons need certain E to provide f (E= hf), energy needed is same for a certain atom, all energy of photon is absorbed, 1 to 1 interaction between photon and e-

Physics A Level Better One (7 decks)

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