AQA AS-Level Physics: Wave-Particle Duality and the Photoelectric Effect

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What is the photoelectric effect?
Where electrons are emitted from a metal if light of a high enough frequency is shone onto it. This is because the electrons absorb energy, when enough is absorbed, the bonds holding them in place break.
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What are the names of the electrons emitted in the photoelectric effect?
Photoelectrons
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What is the threshold frequency?
The minimum frequency of electromagnetic radiation required for photoelectrons to be emitted.
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What influences intensity and kinetic energy of the photoelectrons emitted?
The kinetic energy is influenced by the frequency of light, whilst the intensity is influenced by the number of photoelectrons emitted per second.
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What is the work function of a metal?
The minimum energy needed to break the bonds holding an electron in place. It is the minimum amount of energy required for a photoelectron to be emitted.
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How do we calculate the threshold frequency?
Work function/Planck's constant
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What is the stopping potential?
The potential difference needed to stop the fastest moving electrons with the maximum kinetic energy.
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How do we calculate the maximum kinetic energy of a photoelectron using the idea of stopping potential?
Charge of an electron * stopping potential
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Why must the energy of the photon absorbed to excite an electron be exactly the same as the difference between the two energy levels?
Because energy levels are definite and precise.
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What does the term electronvolt actually mean?
The kinetic energy carried by an electron after it has been accelerated through a potential difference of one volt.
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What is first ionisation energy?
The amount of energy needed to remove an electron from an atom from the ground state.
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How does a fluorescent light work (Comes in a few parts)?
A high voltage is applied across the mercury vapour inside the light. This accelerates free electrons which ionise some of the mercury atoms, producing more free electrons. These electrons collide with electrons in more mercury atoms, exciting them .
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How does a fluorescent light work?
As these electrons return to their ground states, they emit photons in the UV range. The phosphorus coating inside the tube absorbs these photons, exciting its electrons. These electrons cascade down the levels, emitting photons as visible light.
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Why must pressure be low in a fluorescent tube?
So that the electrons can move.
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What is line emission spectra?
A series of bright lines against a black background. Each line corresponds to a particular wavelength of light emitted by the source
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Why does white light produce continuous spectra?
All wavelengths of EM light are found in white light, so all the emitted electrons correspond to each wavelength.
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What is line absorption spectra and how does it work?
As a cool gas passes through light with a continuous spectrum of energy, most of the electrons are in their ground state. This means that these electrons absorb photons with energies equal to the difference between energy levels, causing excitation.
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What is line absorption spectra and how does it work (#2)?
These wavelengths are then missing from the continuous spectrum when the gas comes out the other side. Black lines then correspond to the absorbed wavelengths.
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What is wave-particle duality?
The idea that if wave-like light can show particle properties, then particles like electrons can show wave-like properties.
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What is the calculation for De Broglie's wavelength and what are his ideas based on?
De Broglie's Wavelength = Planck's constant / (mass*speed). His ideas are based on probability waves.
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What can electrons do that provides evidence of wave-particle duality?
They can be diffracted and produce diffraction patterns.
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More widely spaced rings in a diffraction pattern is caused by what two factors?
An increase in wavelength and a smaller accelerating wavelength.
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A more tightly packed diffraction pattern is caused by what two factors?
Increase in speed and an increase in mass.
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Diffraction can only occur when a particle interacts with an object...
about the same length as the De Broglie Wavelength.
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Other cards in this set

Card 2

Front

What are the names of the electrons emitted in the photoelectric effect?

Back

Photoelectrons

Card 3

Front

What is the threshold frequency?

Back

Preview of the front of card 3

Card 4

Front

What influences intensity and kinetic energy of the photoelectrons emitted?

Back

Preview of the front of card 4

Card 5

Front

What is the work function of a metal?

Back

Preview of the front of card 5
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