Photoelectric Effect

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Photoelectric Effect

• By. Brandi Decker, Cody Sweeney, Jessy Godin

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Intro to Photoelectric Effect

• Discovered by Heinrich Rudolf Hertz in 1887.
• Photoelectric Effect The ejection of electrons
  by ultraviolet light in negatively charged matter
  ( ex Zinc)
• The relationship between the number of photons
  and intensity, and between the energy of a photon
  and frequency are the main parts to understanding
  the photoelectric effect.
• Photons The quantum of electromagnetic energy,
  regarded as a discrete particle having zero mass,
  no electric charge, and an indefinitely long.

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Dependants

• The maximum energy of electrons that have been
  ejected is dependant only on the frequency the
  intensity has no affect.
• There is a threshold frequency that must met in
  order for electrons to be ejected.
• The number of electrons ejected is dependant on
  the intensity of the light striking the emitter.
  (The negatively charged matter)

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Electrons being ejected
UV light with frequency meeting threshold
Negatively charged matter
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Example

• If the light hitting the negatively charged
  matter has a high frequency and a low intensity
  will it have a high number of electrons ejected,
  or low number of electrons ejected? Will the
  kinetic energy be high, or low?

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Photoelectric Effect Simulation

• http//phet.colorado.edu/en/simulation/photoelectr
  ic
• From this we can see that as we increase the
  intensity, the current flow also increases.
• And when we increase change the frequency, the
  current flow also changes.
• When we change the polarity of the voltage
  source, the speed of the electrons vary depending
  on how we change the polarity.

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Equation

• Ek hf
• Kinetic Energy (Plancks constant)(Frequency)
• Note Frequency of light is found by speed of
  light (m/s)
• Example
• h 6.626 x10 Js
• f 7.6 x10 Hz
• Ek (6.626 x10 Js)(7.6 x10 Hz)
• Ek 4.76 x10 J

_________________
wavelength (nm)
-34
15
15
-34
-18
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Video Experiment

• http//www.youtube.com/watch?vmuxRZ1irsrk

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Questions

• What is the relationship between the intensity of
  light to the frequency of light?
• Why is there a minimum frequency required?
• Does doubling intensity release more electrons
  form a zinc sheet?

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Answers

• 1. Increasing the intensity of the light beam
  increases the number of photons in the light
  beam, and thus increases the number of electrons
  excited, but does not increase the energy that
  each electron possesses. The energy of the
  emitted electrons does not depend on the
  intensity of the incoming light, but only on the
  frequency of the light.
• 2. Because frequency determines photon energy,
  which is used to knock out an electron from the
  surface, and a minimum amount of energy is
  required to knock out an electron, it is the
  threshold that needs to be reached.
• 3. No, because doubling the intensity simply
  increases the number of photons, it does not
  change their energy.