Photoelectric Effect

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What is a Photon ?
A Photon is a Quantum of Energy of Electromagnetic Radiation
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What is a Quantum ?
A single packet of EM Radiation.
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What does each factor in E=hf=hc/λ mean ?
E= energy carried by one of wave-packets, h=Plancks constant, f= frequency, c=speed of light in a vacuum, λ= wavelength.
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What is the speed of light in a Vacuum ?
3.0x10^8
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What is the charge of a Photon ?
A photon doesn't have a charge.
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What is Photon energy normally given in ?
Usually given in Electronvolts.
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What is the definition of an Electronvolt ?
The kinetic energy gained by an electron when it is accelerated through a potential difference of 1 volt.
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What is the equation which relates to the definition of an Electronvolt ?
eV=1/2mv^2
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What is the experiment to find Planck's constant ?
Start with no current in a circuit with variable resistor then LED with Voltmeter over it ad milliammeter. Adjust variable resistor till LED just turns on. Repeat with different coloured LED, Different wavelength. Plot graph V0 to 1/λ. gradient =hc/e
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What is the Photoelectric effect ?
If you shine EM waves of a high enough frequency onto a surface of a metal, it will instantaneously eject electrons which escape from Photons from the EM source.
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What experiment demonstrates the Photoelectric effect ?
The gold leaf electroscope, has a metal plate initially negatively charged so the gold leaf is repelled. The zinc plate is exposed to UV light and the photoelectric effect causes its free electrons to be ejected. This causes leaf to drop.
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Which 2 conclusions don't work with the wave theory ?
No photoelectrons are emitted if the radiation has frequency below the threshold freq. Photoelectrons are emitted with a variety of KE, value of MaxKE increases with Freq not affected by intensity.
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What are the key points of the Photon model explaining the Photoelectric effect ?
When light hits its surface the metal gets bombarded by Photons, If one of these Photons is absorbed by a free electron the electron will gain energy equal to hf.
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How does the Photon Model explain the Threshold Frequency ?
If the energy gained by an electron from a photon is greater than the work function, the electron is emitted. If there isn't the metal would heat up but no electrons emitted.
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What is the equation to calculate the Threshold Frequency ?
f=Φ/h
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What is the definition of the work function,Φ ?
Work function is the minimum quantity of energy required to remove an electron from the surface of a given solid.
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What does this hf=Φ+KEmax ?
hf represents the energy of the Photon. Φ represent energy needed to escape metal, KEmax is kinetic energy the escaped electron has.
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How to calculate the KEmax ?
use Kinetic energy equation 1/2 m Vmax^2, Velocity is max velocity.
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What is the relationship between Intensity and Kinetic Energy ?
Kinetic energy of the electrons is independent of the intensity of the radiation, because they can only absorb one photon at a time.
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What does the Photoelectric effect actually show ?
It shows how light behaves as a particle.
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Other cards in this set

Card 2

Front

What is a Quantum ?

Back

A single packet of EM Radiation.

Card 3

Front

What does each factor in E=hf=hc/λ mean ?

Back

Preview of the front of card 3

Card 4

Front

What is the speed of light in a Vacuum ?

Back

Preview of the front of card 4

Card 5

Front

What is the charge of a Photon ?

Back

Preview of the front of card 5
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