Regarding BJT, forward active mode of operation i don't seem to get something.
I will use NPN type.
In the forward active regime, Vbe>= 0.75 V, so electrons flow from the emitter through the base .Ok, what i do not understand is why if Vbc <= 0.75 V there is a current Ic = Beta\*Ib, how come electrons flow from emitter to collector if that part of the transistor is "closed" (Vbc <= 0.75)

![schematic](https://i.stack.imgur.com/hqH7r.png)

[simulate this circuit](/plugins/schematics?image=http%3a%2f%2fi.stack.imgur.com%2fhqH7r.png) – Schematic created using [CircuitLab](https://www.circuitlab.com/)