The apparatus is a vessel containing a low pressure gas. A voltage of 10,000 volts produces a discharge in the gas. Electrons are separated from the atoms of the gas and are accelerated toward the positive anode.
A beam of electrons passes through the slit and is made visible by allowing it to hit the slanted glowing ribbon.
What can we see?
1. See the bright green stripe produced by the electron beam hitting the fluorescent ribbon.
2. Notice the pale green stripe where the electron beam strikes the glass envelope.
3. See how the electron beam widens as it travel toward the right, this is because electrons repel each other.
Use the horse shoe magnet so that its jaws straddle the electron beam.
1- The electron bean is bent by the magnetic field of the magnet
2- Reverse the horse shoe magnet; see how the electron beam is bent in the opposite direction
3-Try other positions of the magnet, observe the effects.
The force bending the electron beam is the Lorentz force
where q is the charge, is the velocity and is the strength of the magnetic field.
The direction of the force can be found using the right hand rule as shown here: