does + or - potential connect to the cathode in a vacuum tube?

Question

explain your answer

Answer 1

The cathode must be at a negative potential relative to the anode, for electrons to flow through the tube. A positive anode will attract negatively charged electrons from the cathode.

Even though it is electrons that are the current carrier within the tube, we still use a convention of 'positive' charge flow to indicate current (i.e. conventional current). Maybe that's where your confusion lies.

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Answer 2

The basic function of a cathode is to emit electrons in the evacuated tube so that the emitted electrons are attracted by anode to form as anode current. Hence for the liberation of electrons negative potential is connected to the cathode and anode is connected to positive potential so that it attracts the emitted electrons from the cathode.