A cathode ray tube is made of glass with a small amount of some kind of gas in it. It has metal electrodes at each end to pick up an electric current. The electrodes are named "positive” and "negative." What are one of the main uses of this device ?

to speed up the flow of current flowing through a wire
to examine a beam of charged particles
to magnetize different atoms within a space
to change the strength of a proton within an atom