quantum physics Flashcards

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1
Q

describe experiment which can be used to estimate the value of the Planck constant

A
  • LED will only allow current to pass after a minimum voltage has been put across it
  • at this voltage all the electrons will have the same energy as a photon emitted by the LES which you know the frequency of
  • finding the threshold voltage by seeing when current flows in the circuit can then be used to find h = e/f
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2
Q

describe how to improve the accuracy of the estimate of this experiment

A
  • to improve accuracy of experiment the experiment can be repeated with a variety of different coloured LEDs which each emit different wavelength of light
  • the values of wavelength and threshold pd for each can be recorded and a graph drawn of v against 1/lambda
  • the gradient of this graph will be equal to hc/e
  • as the speed of light and the electron charge are known constants can calc h from this
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3
Q

photoelectric effect

A

phenomenon where shining light with enough energy onto a metal releases electrons and can cause current to flow. the electrons emitted are called photoelectrons

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4
Q

which features of the photoelectric effect can’t be explained if light is a wave

A

if light was a wave then the energy of the electrons released would increase with increasing intensity if the light - but this isn’t the case. instead the energy of electrons depends on frequency and no electrons are released below a certain threshold value no matter how intense the light is

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5
Q

how does the photon model of light explain the threshold frequency seen in the photoelectric effect

A

each electron absorbs a single photon. this single photon must have enough energy for the electron to be released, it it doesn’t the energy is re-emitted. the electron can’t build up energy as It could if light was a wave

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6
Q

true or false: the rate of emission of photoelectrons is proportional to intensity

A

true

higher intensity means more photons, this means more electrons can absorb energy and be released

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7
Q

does the maximum ke of a released electron depend on the intensity of light hitting the surface

A

no, energy transferred is due to a one-to-one interaction and so depends on frequency not intensity

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8
Q

what experimental evidence appears to show particles behaving as waves

A
  • electron diffraction
  • electrons will diffract is passed through the spaces between atoms in graphite
  • this wouldn’t happen if electrons were behaving as particles only
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9
Q
A
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