•Learning Objective:

The Electron Gun

Describe thermionic emissionExplain the process of an electron gunState the factors which affect the deflection of an electron beam

Write down everything you know about..

ELECTRONS

As the _________ increases, thermionic _______ occurs. An atom changes into an ___ emitting an _________.

Defining Words

Thermionic emission.

Therm- is a prefix relating to heat.

-ionic is referring to ions, or charged particles, in this case an electron.

Emission means giving out.

Electron gun

cathode

grid

anodes

y-plates

x-plates

fluorescent screen

Can you label the parts of the gun?

Heated by 6V supply.Greater voltage of 4000V, ACCELERATES electrons to high speeds.

Operation• The electrons are first ‘evaporated’ from a hot cathode

(negative electrode) - similar to the tungsten filament in a low-voltage light bulb (thermionic emission)

• The resulting cloud of electrons is attracted towards a high-voltage anode (positive electrode)

• A hole at the end of the anode allows a proportion of the rapidly moving electrons to ‘shoot’ through, producing an electron beam

• Once created by the gun, the electron beam proceeds through a vacuum inside the tube until it collides with a fluorescent screen.

• Here, energy from the electron beam is released in the form of light, indicating the presence of the beam

How does it work?

Hot metal filament emits electrons

The electrons are attracted to the anodes and accelerated

Electron beam passes through the X and Y plates

Electrons strike the fluorescent screen and seen as a spot of light

Uses of electron beams?

Oscilloscopes

TV tubes

Monitors

X ray productionElectroplating

Combustion engines

Questions

1. In an electron gun explain why:

a the cathode is heated

b the electrons accelerate from the cathode to the anode

c there is a hole in the anode

d there is a vacuum in the container.