Particles of light

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  • Created by: Ami_Bull
  • Created on: 07-03-16 13:18
How do photovoltaic cells work?
The electrons in the material absorb photons and they're released
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Name two things that use light sensitive cells
CDs and barcode scanners
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What is a CCD device?
A grid of thousands off photodiodes that absorb photons from light and emit electrons
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Where are CCDs found?
Digital cameras, astronomical telescopes and digital X-ray machines
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What does CCD stand for?
Charged coupled devices
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What properties of light does the wave theory explain?
Reflection, refraction and diffraction
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How can the photoelectric effect be demonstrated?
A clean sheet of zinc is placed on a negatively charged gold leaf electroscope. UV light is directed on the leaf and the electroscope discharges. However if the leaf is positively charged it remains charged
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What does the photoelectri effect demonstration prove?
That the UV light kocks electrons off the metal surface and are released as photoelectrons
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What is thermionic emission?
When a strong light source is directed at a heated metal wire the electrons gain enough energy for them to escape the attractiv forces of the wire
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Using wave theory what shoul happen if you shon a bright white light on a metal
After a small delay the light would heat the metal and release electrons
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Define quantum of light
A small indivisble package of energy
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E-energy of a photon(J) h-plancks constant(Js) f-frequency of light(Hz)
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What did planck suggest?
That one photon reacts with one electron and the photons energy is absorbed by the eletron
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Define threshold frequency
The minimum frequeny of light required to cause the photoelectric effect
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Defin intensity
the rate of enrgy transfer per unit area
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Define photoelectron
and electon emitted during the photoelectric effect
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If the frequqency is below the threshold frquency what happens?
No photoelectrons are emitted
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What materials can visible lights remove photoelectrons from?
alkali metals, alcium, barium
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What happens if you increasae the intensity of light?
More photoelectrons are emitted(as long as the threshold frequency is met)
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What is the potential well?
A model to help us understand why electrons require energy to remove them from a metal. An electron has its least potential enrgy in the potential well
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What kind of force is in the potential well
Electrostatic attraction
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What does the depth of the well represent
The minimum energy required for electrons to escape a metal
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What requires least energy? Releasing electrons from the surface of the metal or deep in the metal?
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Define threshold energy
The minimum amount of energy required to cause the photoelectric effect
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As light intesity increases what happens to the photoelectrons?
More are emiited but the energy of each one stays the same
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What is the maximum kinetic energy?
The difference between the threshold energy and the photons energy
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Define work function
The minimum energy needed to release a photoelectron from a material. This is equal to the threshold frequency
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hf=ϕ + 1/2mv ²
h-plancks constant(Js) f-frequency of radiation(Hz) ϕ-work function of a material(J) m-mass v-maximum velocity
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What does hf equal?
Energy of a photon
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What does 1/2mv² equal?
Maximum kinetic enrgy of a photon
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Define semiconductor
a material with a conductivity between a metal and an insulator
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What is the name given to materials with a low work function?
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What material can visible light and infrared light cause photoelectrons to be emitted?
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Where are semiconductors found?
CCD devices in digital cameras and in photovoltaic cells
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What happens when light strikes a photoelectric cell?
Photoelectrons are emitted for some wavelengths of light. They are then detected by a photosensitive ammeter
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Define stopping potential
When the electrode is negative which so they electrons do not reach it, the current is zero
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When is diffraction greatest?
When the wavelength of the wave is roughly equal to the size of the gap it passes through
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λ-wavelength(m) h-plancks constant(Js) m-mass of particle(kg) v-velcoity of particle(ms-1)
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Define wave-particle duality
the idea that matter/radiatiom can be described best by using either particle/wave models
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Other cards in this set

Card 2


Name two things that use light sensitive cells


CDs and barcode scanners

Card 3


What is a CCD device?


Preview of the front of card 3

Card 4


Where are CCDs found?


Preview of the front of card 4

Card 5


What does CCD stand for?


Preview of the front of card 5
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