When VidGuy says "emitter has a higher potential than base" he is demonstrating a theoretical cutoff mode at the junction level. He is not applying the transistor to a wired circuit. So he is correct at the junction level of discussion, but you cannot put that transisor into a conventional circuit and say "can you show me that again?"
Don't forget, a transistor conducts depending on base current, not voltage.
And don't get me going about 'conventional current' flow versus 'electron current' flow. Electricity is electrons, not holes.
That is absolutely wrong! A BJT by itself is a transcondance amplifier (voltage controls current), just like a vacuum tube and FET. I have heard folks say to me many times, "You can look at it two ways, voltage or current." Then they try to show that when they drive the base with a current supply, the collector current shows a rather linear relationship within a reasonable range . "That proves a BJT is a current controlled device, right?" Wrong! They are ignoring the physicsof the BJT.
Take a NPN. The emitter is highly doped with N-material and has plenty electrons itching to diflfuse into the very thin P-base and fill up those holes. When they do, they leave behind positive ions in the emitter and create negative ions in the base. This creates an increasing back-voltage that stops the migration when a equilibrium is reached. By applying a positive voltage to the base, the back-voltage is lowered and the charge carriers (electrons in this case) can whiz through the very thin base (human hair size) and be sucked up by the higher voltage of the collector. Unfortunately, some of the electrons that meke up the collector current get diverted into the base circuit by the positive base voltage. This causes a waste current to exist in the base circuit that does absolutely nothing to control lthe collector current. The higher the transistor beta, the less waste current. Fortunately or not, this waste base current is proportional to the collector current and fools a lot of folks into thinking the base current is controlling the collector current when it is not. It is the voltage on the base terminal that is controlling the collector current by modulating the back-voltage of the emitter-base junction. The physics ofthe transistor determine what is controlling the collector.
Now, when you hook up a current source to a BJt, you are in effect insereting a high voltage source in series with a big fat resistor value into the base circuit. That is what a current source is. So you don't have a simple transistor anymore. Instead you have a transistor CIRCUIT. You can make just about anlything with voltage amplifiers (op-amps), true current amplifiers (magnetic amplifiers), BJTs, FETS, vacuum tubes (transconductance amplifiers) by incorporating them into a
circuit. That is what folks are doing when they attach a current generator to the base of a BJT. They are making a current amplifier curcuit, but the transistor itself is still controlled by the
voltage of the current source.