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AS Physics > Chapter 3 > Flashcards

Chapter 3 Flashcards

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1
Q

Describe the photoelectric effect

A

The emission of electrons from the surface of a material due to exposure of the material to electromagnetic radiation

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2
Q

Briefly describe the key points in the experimental observations of the photoelectric effect

A
  • There is a threshold frequency
  • There is a variation of the threshold frequency
  • There is an affect of the radiation intensity
  • There is a time of emission
  • There is a minimum KE of photoelectrons
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3
Q

Observations of photoelectric effect: Expand on the “threshold frequency”

A

The photoelectric effect only happens if the frequency of the EM radiation is above a certain value

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4
Q

Observations of photoelectric effect: Expand on the “variation of the threshold frequency”

A

Different materials require different amounts of energy to release electrons. TF varies with materials

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5
Q

Observations of photoelectric effect: Expand on the “affect of radiation intensity”

A

The greater the intensity, the greater the number of electrons emitted, but only if the radiation is above the threshold frequency

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6
Q

Observations of photoelectric effect: Expand on the “time of emission”

A

Electrons were emitted as soon as the material was exposed

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7
Q

Observations of photoelectric effect: Expand on the “minimum KE of photoelectrons”

A

Depends only on the frequency of the EM radiation and the material exposed, not the intensity

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8
Q

What are the problems with the wave theory which the photoelectric effect has?

A

Wave theory predicted that:

  • No threshold frequency -> All frequencies of radiation should eventually cause emission
  • Increasing intensity should increase emission of all frequencies -> Not just those >threshold
  • Emission wouldn’t take place immediately -> weaker radiations would take longer to produce electrons
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9
Q

What is Einstein’s explanation for the photoelectric effect and the clashes with the wave theory?

A
  • EM radiation consists of photons
  • Energy of photons depends on frequency of radiation ONLY. This energy is proportional to E=hf
  • Photons interact with one to one interaction with electrons with the material
  • If photon energy > certain amount, an electron would be emitted, and excess energy goes into electron KE
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10
Q

What is the work function in: hf = Φ + EK max?

A

The minimum amount of energy needed for an electron to escape the surface

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11
Q

What is stopping potential?

A

The minimum potential to stop photoelectric emission.

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12
Q

What is an ion?

A

A charged atom

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13
Q

How are ions created?

A

By adding or removing electrons

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14
Q

How can ionisation be caused?

A
  • Nuclear radiation
  • Heating
  • Passing an electric current through a gas
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15
Q

What is an electron volt?

A

A unit of energy equal to work done when an electron is moved through a p.d of 1V

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16
Q

What is ionisation energy?

A

The energy required to remove one electron from an atom

17
Q

What is excitation?

A

The promotion of electrons from lower to higher energy levels within an atom

18
Q

In excitation, where do electrons move in relation to the shell?

A

Electrons move from an inner to an outer shell

19
Q

What is some of the KE of an incoming electron used to do in excitation?

A

Used to move the electron to a higher energy level

20
Q

How many excitation states and energies to atoms have?

A

Multiple

21
Q

How are electrons bound to the nucleus of an atom?

A

EM attraction

22
Q

What is the ground state?

A

The energy level of an electron occupying the nearest possible position to the nucleus

23
Q

What is the lowest possible energy level for an electron called?

A

The ground state

24
Q

How many electrons can exist in the lowest possible energy level?

A

2

25
Q

How are energy levels measured?

A

In respect to ionisation energy, which is assigned 0eV

26
Q

If the ground state has an energy level, what is true about all other energy levels?

A

They are negative

27
Q

When are electrons considered to be in ionisation state?

A

When their energy levels are above the ground state but below the ionisation level

28
Q

How stable are excited states?

A

very unstable

29
Q

How long does it take an electron to fall back to a lower energy level?

A

about 10^-6s

30
Q

What happens when an electron falls through energy levels?

A

A photon of EM radiation is emitted

31
Q

What is de-excitation?

A

When an electron moves from a higher to lower energy level (and a photon is emitted)

32
Q

What is true about the energy of a photon emitted in de-excitation?

A

It is equal to energy lost by the electron

33
Q

What is a fluorescent tube?

A

A glass tube with a fluorescent coating on its inner surface. Contains mercury vapour at low pressure

34
Q

Why does light have a dual nature?

A

It can behave as a particle and a wave

35
Q

How is the wave-like nature of light observed?

A

Through diffraction

36
Q

How is the particle-like nature of light observed?

A

Photoelectric effect

AS Physics (12 decks)

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