AS physics- Electromagnetic Radiation and Quantum Phenomena

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Flashcards by lolly.robinson1, updated more than 1 year ago
lolly.robinson1
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Flashcards on AS physics- Electromagnetic Radiation and Quantum Phenomena, created by lolly.robinson1 on 04/10/2015.

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Question Answer
What is the photoelectric effect? Free electrons on the surface of a metal absorb energy from the light and vibrate. If an electron absorbs enough energy, the bonds holding it to the metal break and it is released. The electron emitted are called photoelectrons.
What three conclusions were drawn from the experiment? 1) No photoelectrons are emitted if the radiation had a frequency below the threshold frequency. 2) Photoelectrons are emitted with a variety of kinetic energies ranging from 0- maximum value. The maximum kinetic energy increases with the frequency of the radiation and is unaffected by intensity. 3) No. of photoelectrons emitted is proportional to the intensity of radiation.
What is the threshold frequency? If the frequency is below this value, no photoelectrons are emitted.
What is meant by the work function of a metal? Before an electron can leave the surface of a metal, it needs enough energy to break the bonds holding it there. This is called the work function energy.
What is line emission spectra? If you split the light from a fluorescent tube with a prism, you get a line spectrum, seen as a series of bright lines against a black background. Each line corresponds to a particular wavelength. Since only certain photon energies are allowed, you only see the corresponding wavelengths.
What is an absorption spectrum? Shining white light through a cool gas gives an absorption spectrum. Contains all possible wavelengths Hit things emit a continuos spectrum in the visible and infrared.
How do fluorescent tubes produce visible light? Fluorescent tubes contain mercury vapour, across which a high voltage's applied. When free electrons and mercury electrons collide, they're excited to higher level. when these electrons return to their ground states, they release photons in the UV range. A phosphorus coating on the inside of the tubes absorbs the photons, exciting the electrons to much higher levels. As these electrons cascade back down the energy levels, emitting lower energy photons in the form of visible light.
Which observations show light to have a "wave- like" character? It produces interference and diffraction patterns which can only be explained using waves interfering constructively.
Which observations show light to have a "particle-like" character? A beam of light is like a series of particle- like photons. If a photon of light is a discrete bundle of energy, then it can interact with an electron in a one-to-one way. all the energy in the photon is given to one electron.
Which observations show electrons to have a "wave-like" character? Diffraction patterns are observed when accelerated electrons in a vacuum interact with the spaces in a graphite crystal. The slower the electrons, the wider the diffraction pattern.
An electron and a proton are accelerated from rest by the same potential difference. Why will they have different wave lengths? Same kinetic energy is voltages are equal. Proton = larger mass so smaller speed kinetic energy is proportional to the square of the speed and momentum is proportional to the speed, so they have different momentums. Wavelength depends on momentum, so the wavelengths are different.
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