GCSE Physics P3 - Electron beams

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What are X-rays?
High energy EM waves with a high frequency and short wavelength. They are a form of ionising radiation.
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What is thermionic emission?
Electrons are provided with enough energy to escape the outer shells of their atoms - they are 'boiled off' the filament
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What is the cathode made of and why?
Tungsten is often used because it can stand high temperatures. It is coated in strontium and barium because they are good electron emitters
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Why is a voltage needed across the cathode (filament) in a simple electron gun?
To provide the ionisation energy to the electrons due to the heating effect of the current
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What voltage is put through the cathode and why?
6V, to provide the energy needed for thermionic emission
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What voltage is put through the anode and why?
300V, to create a large potential difference
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Why is a high voltage (p.d) needed between the cathode (-) and the anode (+)?
To accelerate the electrons by repelling them from the cathode and attracting them to the anode.
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Why is there a vacuum in the electron gun?
So there are no particles in the way for the electrons to collide with. Electrons are accelerated straight across and KE is conserved
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What is the name given to the beam of electrons in the electron gun?
Cathode rays
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If the anode (+) is used as a metal target, what is produced?
X-rays
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Why does the anode have a hole in it?
It focuses the electron beam into a cathode ray
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Why are X-rays produced when the anode (+) is used as a metal target?
The kinetic energy of the electrons is converted to X-rays on collision
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Why would the electron gun not work if the cathode and anode were switched?
The emitted electrons would be attracted to the positively charged filament and would not produce cathode rays
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What is this set up called a diode valve?
Current only flows one way around
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What is an electric current?
The rate of flow of negative charge
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Why are the cathode rays equivalent to an electric current?
Cathode rays are a beam of electrons. Electrons are negatively charged particles and these move within the apparatus
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What is the electron gun equation?
The work done by the electric field = kinetic energy gained by the electrons
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The electron gun equation can also be written as
KE = eV = 0.5mv*2
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What does 'V' stand for and what is it measured in?
Voltage in Volts
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What does 'v' stand and what is it measured in?
Velocity in metres per second (m/s)
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Other cards in this set

Card 2

Front

What is thermionic emission?

Back

Electrons are provided with enough energy to escape the outer shells of their atoms - they are 'boiled off' the filament

Card 3

Front

What is the cathode made of and why?

Back

Preview of the front of card 3

Card 4

Front

Why is a voltage needed across the cathode (filament) in a simple electron gun?

Back

Preview of the front of card 4

Card 5

Front

What voltage is put through the cathode and why?

Back

Preview of the front of card 5
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