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Physics > Quantum Physics > Flashcards

Quantum Physics Flashcards

1
Q

What is the basic principle of Quantum Physics

A
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2
Q

What phenomenon brought up the field of Modern Physics as it disputed Classical Physics theories?

A

The Photoelectric Effect

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3
Q

What phenomenon provides evidence that particles can have wave-like properties?

A

Electron Diffraction

Electrons travelling through polycrystalline graphite will be diffracted by the atoms and the spacing between the atoms.

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4
Q

What are the apparatus needed in an electron diffraction experiment?

A

A beam of electrons, a detection screen, and a graphite film

The layered-like structure of graphite allows it behave like a diffraction grating

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5
Q

What can electron diffraction be used for?

A

To determine the arrangement of atoms in matter and the size of nuclei.

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6
Q

How does

the Photoelectric Effect dispute Classical wave theory?

A

It proves that the emissionof electrons is dependent on the frequencyof the wave and the no. of e- is dependent on the energy of the wave

Classical wave theory would have suggested that the reverse is the case

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7
Q

What then is proportional to

the wave intensity in the Photoelectric Effect?

A

The Photoelectric current

This is the number of photoelectrons emitted per second

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8
Q

What is

the Photoelectric Effect?

A

The emission of e- from the surface of a metal when radiation is incident on it

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9
Q

What is the prerequisite

for incident radiation to liberate photoelectrons from metals?

A

The frequency of the incident radiation must be ≥ the threshold frequency of the metal

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10
Q

What is

Threshold frequency?

A

Theminimum frequency of the incident radiation on a metal’s surface needed to liberate photoelectrons from it

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11
Q

What is

Threshold wavelength?

A

The maximum wavelength of the incident radiation on a metal’s surface needed to liberate photoelectrons from it

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12
Q

Do all the emitted photoelectrons have the same KE when liberated?

A

No

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13
Q

Which photoelectrons typically have the highest (maximum) KE?

A

The valence electrons of surface atoms

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14
Q

What happens to the leaf of a gold-leaf electroscope when -vely charged metal plate is irradiated by light of a sufficient frequency to release photoelectrons?

A

The leaf falls

When photoelectrons are emitted, the -ve plate loses its -ve charge

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15
Q

Will any change to the leaf of a gold-leaf electroscope be observed when the metal plate is given a +ve charge?

A

No

As photoelectrons are emitted, the +ve charge of the plate creates an attractive force between the electron and the metal plate, preventing them from being liberated

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16
Q

What is Einstein’s photoelectric equation?

A

(Total) Σ = hf0 + KEmax.

The total energy of the incident radiation is equal to the energy needed to liberate the electron from the metal and the maximum KE it can get on liberation

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17
Q

What is a photon

A

A packet (or quantum) of energy possessed by an EM wave

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18
Q

What is the implication of the Photon model of a wave

A

It implies that waves can have particle-like properties

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19
Q

What are the particle-like properties of waves?

A
  1. Elements of it (photons) collide elastically with e- to liberate photoelectrons
  2. Elements of it (photons) possess momentum
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20
Q

What is the relationship between a photon and an electron

in the Photoelectric Effect under the Photon model of a wave?

A

It is a one-to-one relationship

One electron absorbs the energy of one photon and it is liberated if this Σ value is greater than hf0

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21
Q

What happens to the photon when it collides with an electron?

A

The electron absorbs its energy and it ceases to exist

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22
Q

What happens when the Σ supplied by the photon is less than hf0?

A

The electron absorbs its energy and it as KE

which it can lose upon collision with metal ions

23
Q

What is the work function (Φ) of a metal?

A

This is the energy required to liberate e- from the surface of a metal

Each metal has their own w0 (another way of representing work function) value

24
Q

Why is the value of the KE of photoelectrons up to a maximum?

A

For e- that are not as loosely bounded, work is done against the attractive forces of the nucleus to bring the electron to the surface, hence its emission energy will be reduced

25
Q

What unit is used to better express photon energies?

A

The electron-volt

26
Q

What is electron-volt?

A

The work done in accelerating an electron through a PD of 1 volt

27
Q

What is the value of one electron-volt in Joules?

A

1.6 x 10-19 J

28
Q

How does KEmax. relate to stopping potential?

A

The value of Voltage that gives the maximum KE is the PD required to stop emitted photoelectrons from leaving the surface of the metal

29
Q

What are

Energy Levels?

A

Specified regions of space around an atom where its e-can be found

they are quantised energy states within the atom

30
Q

What is

the ground state of an element?

A

The state at which the atom possesses the least amount of energy with all the e- in their lowest energy state

31
Q

What are the 2 main characteristics of

Energy Levels?

A

They are fixed and are peculiar to each element

32
Q

What is required for

an e- to transit between 2 energy levels?

A

It has to absorb the exact amount of energy needed for a specific transition

E.g. if an electron wanted to move btw Σ levels 2 and 3, it has to absorb Σ equivalent to the energy difference between the 2 levels

33
Q

What happens if

an e- absorbs less or more Σ than what is required?

A

No transition will occur

34
Q

Why do

have energy levels -ve values?

A

Because external energy is supplied to the atom in order to make the transition

35
Q

What is the value in eV

of the ionisation level?

A

0 eV

At ionisation the e- has escaped from the attractive pull of the atom’s nucleus

36
Q

What are all other energy levels apart from the ground state called?

A

Excited states

37
Q

What happens when an electron ‘falls’ from a higher energy level to a lower one?

A

A photon is emitted ; its frequency is equal to the frequency of the energy difference between the 2 levels

38
Q

What equation helps find the energy difference btw 2 energy levels?

A

ΔΣ = hfhigher - hflower

39
Q

How many types of emission spectra are there?

A

Two : Line emission spectrum and Continuous emission spectrum

40
Q

What is

the Line emission spectrum?

A

It is a spectrum that consists of bold, distinct coloured lines, that show the specific wavelengths absorbed (and thus emitted) by electrons in gaseous atoms

41
Q

What is the nature

of the gases that are used to produce the Line emission spectrum?

A

They must be hot

Hot gases are raised past their ground states. e- can absorb energy from the heat to make transitions btw Σ levels

42
Q

What is

the Continuous emission spectrum?

A

It is a spectrum that consists of a wide, continuous range of wavelengths with no clear-cut distinction between the colours.

43
Q

What type of light

produces the Continuous emission spectrum?

A

White Light

44
Q

What is

an absorption spectrum?

A

It is a spectrum that consists of dark lines against the background of a continuous spectrum to show the absence of light of particular wavelengths.

45
Q

How is

an absorption spectrum produced?

A

When white light passes through a substance (such as a cool gas) before being diffracted

46
Q

What do the dark lines

in an absorption spectrum show?

A

The wavelengths absorbed by the electrons in the atoms of a substance when white light is incident on it

47
Q

Why are cool gases at low pressure used when trying to produce an absorption spectrum?

A

When gases are cool, its atoms are more likely to be in their ground state. When gases are at low pressure, its atoms are duly separated from each other

This allows photons interact with electrons on an atom-by-atom basis

48
Q

What does the line emission spectrum of an atom tell us about it?

A

Since there are sharp distinct, coloured lines, electrons in the atom can only exist in specific energy levels.

49
Q

Why do the line emission spectra of different atoms differ?

A

Because they have different spacings between their energy levels

50
Q

Is a photon a particle?

A

No, it is an element of an electromagnetic wave

51
Q

Do photons have mass?

A

No

52
Q

Who suggested that matter can have wave-like properties?

A

Louis de Broglie

53
Q

Who suggested that waves can have matter-like properties?

A

Albert Einstein

54
Q

What is the equation for the de Broglie wavelength?

A

λ = h/p

h = Planck’s constant
p = momentum of the photon

where λ = wavelength

Make sure “de Broglie wavelength” is specified before you use this formula - Mr Onanuga

Physics (3 decks)

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