7.3 Thermionic emission

Question 1

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

Answer 1

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

Question 2

How does thermionic relate to how an electron gun works

Answer 2

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.

Question 3

How is the electron gun usually made

Answer 3

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

Question 4

How are these electron beams used in the classroom

Answer 4

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

Question 5

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

Answer 5

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