The emission of electrons from a metal when light of a high enough frequency is shone onto it
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Describe what happens during the photoelectric effect
The free electrons near the surface of a metal absorb energy from the radiation, making them vibrate. If the electron absorbs enough energy, the bonds holding it to the metal can break and the electron can be released as a photoelectron
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What is the threshold frequency?
The lowest frequency of radiation that when shone on a metal will cause electrons to be released
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What does the frequency of radiation affect?
The maximum kinetic energy of the photoelectrons
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What is the intensity of radiation?
The amount of energy per second hitting an area of the metal; the power per unit area
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What does the intensity of radiation affect?
The number of photoelectrons emitted per second
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What did Einstein suggest about EM waves?
That EM waves (and the energy they carry) can only exist in discrete packets called photons
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What is the work function energy?
The minimum energy needed for an electron to break its bonds and escape the metal's surface
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What is the formula relating threshold frequency and work function?
threshold frequency = work function ÷ Planck constant
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What is stopping potential?
The potential difference needed to stop the fastest moving photoelectrons
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What is the formula for calculating stopping potential?
charge on the electron x stopping potential = maximum kinetic energy
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What is 1 electron volt equal to in joules?
1 eV = 1.6 x 10^-19 J
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Define the electron volt
The kinetic energy carried by an electron after it has been accelerated from rest through a potential difference of 1 volt
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What is excitation?
The movement of an electron to a higher energy level in an atom
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How do electrons move down energy levels?
By emitting a photon ( or photons if they move down more than one energy level)
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How can photons move up energy levels?
By absorbing a photon with the exact energy difference between the two levels
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What is ionisation?
The process where an electron is added to or removed from an atom
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What is ionisation energy?
The amount of energy needed to remove an electron from an atom in its ground state
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What is a line emission spectrum?
A series of bright lines against a black background, where each line corresponds to a particular wavelength of light emitted by a light source
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How do you get a line emission spectrum?
By splitting light from a fluorescent tube with a prism or diffraction grating
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What do line spectra provide evidence towards?
That electrons exist in discrete energy levels; atoms can only emit photons with energies equal to the difference between two energy levels, and since only certain photon energies are allowed, you only see corresponding wavelengths in the spectrum
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What is a line absorption spectrum?
A light spectrum with dark line corresponding to different wavelengths of light that have been absorbed
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How do you get a line absorption spectrum?
By passing white light through a cool gas
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Explain how some wavelengths of light can be absorbed by a cool gas
At low temperatures, most of the electrons in the gas atoms with be in their ground state. Photons of the correct wavelength are absorbed by these electrons to excite them to higher energy levels. These wavelengths are then missing from the spectrum
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Give an example that support the idea that waves have a particulate nature
The photoelectric effect
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Give an example that support the idea that particles have a wave-like nature
Electron diffraction
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Describe the process of electron diffraction
Electrons are accelerated to high velocities in a vacuum and then passed through a graphite crystal; as they pass through the spaces between the atoms of the crystal, they diffract and produce a pattern of rings
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How does changing the speed of the electrons affect the amount of diffraction?
Increasing the electron speed reduces the amount of diffraction (circles become closer together)
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How does changing the mass of the particles affect the amount of diffraction?
Increasing the mass (e.g. by using neutrons instead of electrons) reduces the amount of diffraction (circles become closer together)
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Other cards in this set
Card 2
Front
Describe what happens during the photoelectric effect
Back
The free electrons near the surface of a metal absorb energy from the radiation, making them vibrate. If the electron absorbs enough energy, the bonds holding it to the metal can break and the electron can be released as a photoelectron
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