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Physics > Unit 1: Quantum Phenomena > Flashcards

Unit 1: Quantum Phenomena Flashcards

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0
Q

When does photoelectric emission not take place?

A

When the frequency of the incident electromagnetic radiation is below a certain value known as the threshold frequency and the wavelength of the incident light must be less than a maximum value equal to the speed of light divided by the threshold frequency.

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1
Q

What is known as the photoelectric effect?

A

When electrons are emitted from the surface of a metal as electromagnetic radiation above a certain frequency is directed at the metal.

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2
Q

What does threshold frequency depend on?

A

The type of metal.

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3
Q

What doesn’t matter if the frequency of the incident radiation is smaller than the threshold frequency?

A

The intensity of the radiation.

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4
Q

What is proportional to the intensity of the incident radiation?

A

The number of electrons emitted per second.

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5
Q

How fast does the photoelectric prevail?

A

As soon as the incident radiation is directed at the metal (without delay) no matter how weak the intensity.

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6
Q

What can the wave theory of light not explain?

A

The existence of the threshold frequency or why the photoelectric effect occurs without delay.

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7
Q

What did wave theory incorrectly predict about the photoelectric effect?

A

Emission should take place with waves at any frequency and emission would take longer when using low intensity waves.

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8
Q

What is light composed of?

A

Photons

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9
Q

What is the formula for the energy of a photon?

A

Hf

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10
Q

What is the equation for wavelength?

A

C/f

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11
Q

What happens when light shines onto a metal surface?

A

An electron at the surface absorbs a single photon from the incident light and therefore gains energy equal to hf.

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12
Q

When can an electron leave a metal surface?

A

If the energy gained from a single photon exceeds the work function of the metal.

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13
Q

What is the work function?

A

The minimum energy needed by an electron to escape from the metal surface.

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14
Q

What is the formula for the maximum kinetic energy of an emitted electron?

A

Ekmax = hf - work function

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15
Q

What is the formula for the threshold frequency of a metal?

A

Fmin = work function/h

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16
Q

The energy of each vibrating atom is…

A

Quantised meaning only certain levels of energy are allowed.

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17
Q

What happens when the energy of the photon exceeds the work function?

A

The conduction electron can leave the metal.

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18
Q

What happens if the electron does not leave the metal?

A

It collided repeatedly with other electrons and positive ions and it quickly loses its extra kinetic energy.

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19
Q

What happens when light is directed at the photocathode?

A

Electrons are emitted from the cathode to the anode.

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20
Q

What is proportional to the number of electrons per second that transfer from the cathode to the anode?

A

The reading on the ammeter.

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21
Q

What is the equation for the number of photoelectrons that transfer from the cathode to the anode?

A

I/e where I is the photoelectric current and e is the charge of an electron.

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22
Q

What is the photoelectric current proportional to?

A

The intensity of the light incident on the cathode.

23
Q

What is light intensity a measure of?

A

The energy per second carried by the incident light.

24
Q

What doesn’t the intensity of the incident light affect?

A

The maximum kinetic energy of a photoelectron.

25
Q

How is Ekmax = hf - work function similar to y=mx+c

A

Y=Ekmax, h=gradient, x-intercept=threshold frequency and y intercept=-work function

26
Q

What is the process of creating ions (charged atoms) called?

A

Ionisation

27
Q

What is the equation for the ionisation energy of a gas atom?

A

eV

28
Q

What is the electron volt?

A

A unit of energy equal to the work done when an electron is moved through a pd of 1 volt.

29
Q

What is excitation?

A

This is when atoms can absorb energy from colliding electrons without being ionised.

30
Q

What do the certain energies that excitation can occur at link to?

A

The atoms of the gas.

31
Q

What happens if a colliding electron loses all its kinetic energy when it causes excitation?

A

The current due to the flow of electrons through the gas is reduced.

32
Q

What happens if the colliding electron does not have enough kinetic energy to cause excitation?

A

It is deflected by the atom with no overall loss in kinetic energy.

33
Q

What are excitation energies?

A

The energy values at which an atom absorbs energy.

34
Q

What happens when excitation occurs?

A

The colliding electron makes an electron inside the atom move from an inner shell to an outer shell.

35
Q

What is the excitation energy always less than?

A

The ionisation energy

36
Q

Is the energy of an electron in a shell constant?

A

Yes

37
Q

Which electrons have the most energy?

A

Those that are furthest from the nucleus.

38
Q

What is the ground state?

A

The lowest energy state of an atom.

39
Q

What is the excited state?

A

When an atom in the ground state absorbs energy and one of its electrons moves to a shell of higher energy.

40
Q

Why is the electron configuration in an excited atom unstable?

A

An electron that moves to an outer shell leaves a vacancy in the shell it moved from.

41
Q

What happens when an electron emits a photon?

A

An electron moves to an inner shell to fill in a vacancy. The atom therefore moves to a lower energy level.

42
Q

What is the energy of a photon equal to in excitation?

A

The energy lost by the electron and therefore the atom.

43
Q

What is the equation for the energy of an emitted photon?

A

E1-E2 (E1=higher energy level)

44
Q

What is the condition for an electron to absorb a photon and move to an outer shell?

A

The energy of the photon must exactly equal the gain in the electron’s energy.

45
Q

Why does a fluorescent tube emit visible light?

A

Ionisation and excitation of the Mercury atoms occurs as they collide with each other and with electrons in the tube. The Mercury atoms emit UV photons when they de-excite, the UV atoms are absorbed by atoms of the fluorescent coating which causes excitation of the atoms and then the coating atoms de-excite and emit visible photons.

46
Q

Is a fluorescent tube more efficient than a filament lamp?

A

Yes

47
Q

Are wavelengths of the lines of a line spectrum of an element characteristic to the atoms of that element?

A

Yes

48
Q

Why do elements not produce the same pattern of light wavelengths?

A

The energy levels of each type of atom are unique to that atom.

49
Q

What is proof for the wave-like nature of light?

A

When diffraction of light takes place.

50
Q

What causes greater diffraction?

A

A narrower gap or a longer wavelength.

51
Q

When is the particle-like nature of light observed?

A

The photoelectric effect.

52
Q

Do matter particles have a dual wave-particle nature?

A

Yes

53
Q

What evidence is there that matter has particle-like properties?

A

Electrons in a beam can be deflected by a magnetic field.

54
Q

What evidence is there for matter having wave-like behaviour?

A

The de Broglie wavelength and the diffraction of electrons.

55
Q

What is the equation for the de Broglie wavelength?

A

H/p where p is momentum

Physics (18 decks)

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