7.3 Thermionic emission Flashcards

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1
Q

What happens to the electrons in a metal when a piece of metal is heated to a high temperature

A

Electrons ‘bubble’ out of the surface of the metal. of course however they will be attracted back to the surface by the protons they have left behind

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2
Q

How does thermionic relate to how an electron gun works

A

When the electrons ‘bubble’ out of the surface of the metal, a positively charged place is placed near the metal in a vacuum, the electrons accelerate towards the plate and this can be made into a narrow beam.

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3
Q

How is the electron gun usually made

A

The metal is heated by a resistor connected to a power supply
The narrow beam is made by making a small hole in the positive plate

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4
Q

How are these electron beams used in the classroom

A

They are used in cathode ray oscilloscopes. These type of beams are accelerated in a vacuum through 2000v. Obviously the electrons are moving at very high speeds

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5
Q

How does the force on an electron differ in an electric and magnetic field

A

Force on an electron in an electric field is parallel to the field while the force on the electron in a magnetic field is perpendicular to the field

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