Flashcards
Physics
Flashcards do conjunto (29)
- 1Photoelectric effectIf you shine radiation of a high enough frequency onto the surface of the metal , it will emit an electron. The free electrons absorb energy from the radiation and vibrate. If they absorb enough energy the bonds can break and they can be released.
- 2PhotoelectronsThis is the name given to the electrons emitted from the photoelectric effect.
- 3Threshold frequencyThis is the frequency needed for an electron to be emitted.
- 4Wave theory and threshold frequencyIf electrons were a wave, the EM radiation would give each electron a bit more energy from each wave front and eventually give them enough energy to be removed. If the frequency was lower it would just take longer. Wave theory can't explain threshold frequency.
- 5Frequency on maximum kinetic energyPhotoelectrons are emitted with a variety of different kinetic energies. The maximum kinetic energy increases with the frequency of the radiation.
- 6Intensity on maximum kinetic energyThe intensity is the amount of energy per second hitting an area of the metal. The maximum kinetic energy is unaffected by intensity.
- 7Intensity on number emittedThe number of photoelectrons emitted per second is proportional to the intensity of the radiation.
- 8Wave theory and kinetic energyThe higher intensity of the wave, the more energy it should transfer to an electron. The kinetic energy should increase with intensity but it doesn't so the wave theory doesn't explain the photoelectric effect.
- 9PhotonsEM waves can only be released in small discrete packets called photons.
- 10Demonstrating the photoelectric effect using a UV lamp and a zinc plate attached to the top of an electroscope (a box containing a gold leaf strip)The zinc plate is negatively charged and repels the gold leaf raising it. UV light is then shone on the zinc plate, it loses electrons so therefore no longer repels the gold leaf.
- 11Photon theory and threshold frequency and work functionIf a photon collides with a free electron, the electron will gain the energy equal to E=hf. The energy needed to break the bonds holding the electrons is called the work function. If the energy gained is larger than the work function, an electron can be emitted.
- 12Photon theory and maximum kinetic energyThe kinetic energy the electrons will have the energy hf minus any other energy losses, which causes the difference in kinetic energies. The minimum amount of energy an electron loses is the work function (energy needed to break bonds).
- 13Stopping potentialMaximum kinetic energy can be used to measure the stopping potential. The stopping potential is the potential differenced needed to stop the fastest moving electrons travelling with kinetic energy .
- 14The electron voltDefined as the kinetic energy carried by one electron after it has been accelerated from rest through a potential difference of 1 volt. The energy gained is equal to the accelerating voltage (1.6x10-19 J).
- 15Discrete energy levelsElectrons can only exist in certain energy levels, each given a number, the lowestand electron can be in -the ground state- being 1.
- 16ExcitationThis is when electrons are in a higher energy level than the ground state. They absorb a photon with the energy equal to the difference in energies between the two levels of transition.
- 17De-excitationThis is when electrons move back down energy levels and a photon is emitted. The photo emitted has a certain energy due to the defined energy levels.
- 18IonisationThis is when an electron is removed from an atom. The energy of each energy level shows the amount of energy needed to remove an electron from that level.
- 19Ionisation energyThe energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms. Or the energy needed to remove an electron from the ground state atom.
- 20Photon emission - Fluorescent tubesMercury vapour is contained inside, in which a high voltage is applied accelerating free electrons, ionizing some of the atoms producing more free electrons. They collide with the mercury atoms, exciting the electrons to higher energy levels. When the de-excite they release photons in the UV range. A coating allows the photons emitted to be reduced to visible light.
- 21Line emission spectraSeries of bright lines against a black background. Each line corresponds to a particular wavelength of light emitted by the source. Atoms can only emit photons with energies equal to the difference between the two energy levels. Since only certain energies are allowed, you only see the corresponding wavelengths.
- 22Line absorption spectra- continuous spectraWhite light spectrum is continuous. Hot things emit a continuous spectrum in the visible and infrared. All the wavelegnths are allowed because the electrons are not confined to energy levels, they are all free to move around.
- 23Line absorption spectra- what are line absorption spectra?You get a line absorption spectrum when a continuous spectrum of energy passes though cool gas. At low temperatures, most electrons are at ground state. Photons of the correct energy levels are absorbed causing excitation. These wavelegnths are then missing from the continous spectrum.
- 24Comparing line absorption spectra and emission spectraThe black lines missing from the line absorption spectra are the same to the coloured lines emitted in the emission spectra.
- 25Wave particle dualityLight can act as both waves and particles.
- 26DiffractionA beam of light is shone at a gap and the light spreads out (diffraction). This could only happen if light was a wave. If it was a particle, the light would either not get through the gap, or pass straight through unchanged.
- 27The photoelectric effectLight must be a particle, like a photon. It can then act with an electron in a one to one way. All the energy from the photon goes to one electron.
- 28De Broglie wavelegnthIf wave-like light showed particles properties , particles should be able to show wake-like properties. De Broglie wave can be interpreted as a probability wave.
- 29Electron Diffraction
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- AS - Level AS Physics FlashCards sobre Physics, criado por beckycurtis em 26-03-2016.
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- beckycurtis
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