This is a takeoff from another thread where some people declare voltage to come first followed by current.
As you should know, each application has it's own preferred method or at least each model has it's own requirements. Also, some people are bent on declaring one way of doing it over another but is there really an overall blanket preference? I dont think so.
But i must quote one line from your post in particular:
"That is because we cannot "inject" a current - a current is always the RESULT of an applied voltage"
That's not really true except again in a theory that prefers that definition. We can also say that voltage is the result of a current that flows from one place to another.
I believe the correct way to look at this is that they both occur simultaneously. A way of looking at this is that in order to establish a voltage you must move charge, and charge implies both current and voltage. simultaneously. In other words, energy.
Now it is true that some calculations will prefer one view over the other, but i think it is easy to see how both ideas can play out in real life.
If we "apply" a voltage to an inductor, current flows, but it does not 'start' to flow after the voltage is applied, it starts immediately. But even if we look at it as 'after' then what about the capacitor.
If we "apply" a voltage to a capacitor, we get infinite current flow even with a tiny capacitance. Now we could say that you have to apply a current 'first' in order to charge the capacitor to some voltage, so that the voltage comes 'after' the current. But that' also not right, they both occur simultaneously.
Now we might go as far as to say that the "electric field" is 'first' established in a wire before current can flow. But in that view we are talking about *relative* values of current and electric field. In this case we deem a current as low as 1 femtoampere (for example) to be zero current when really it is not zero. Again it has to be simultaneous. Also we can look at how that electric field got established in the first place.
So the bottom line is that current and voltage are independent only in theory and we decide what theory we want to use.
It's ok to disagree with this but then you should have at least one physical example that demonstrates the contrary.
Hello,Yes - I agree. For switching applications (saturation operation) and for the purpose of finding suitable resistor values it may be easier to view the BJT as a current-controlled device (injecting a base current).
However, each good and experienced engineer knows that the wording "injecting a current" is something like "labor jargon" .
That is because we cannot "inject" a current - a current is always the RESULT of an applied voltage.
In our example: For switching applications, the base current is mainly determined by the large base resistor RB, which forms a voltage divider together with the base-emitter resistance (much samller).
As you should know, each application has it's own preferred method or at least each model has it's own requirements. Also, some people are bent on declaring one way of doing it over another but is there really an overall blanket preference? I dont think so.
But i must quote one line from your post in particular:
"That is because we cannot "inject" a current - a current is always the RESULT of an applied voltage"
That's not really true except again in a theory that prefers that definition. We can also say that voltage is the result of a current that flows from one place to another.
I believe the correct way to look at this is that they both occur simultaneously. A way of looking at this is that in order to establish a voltage you must move charge, and charge implies both current and voltage. simultaneously. In other words, energy.
Now it is true that some calculations will prefer one view over the other, but i think it is easy to see how both ideas can play out in real life.
If we "apply" a voltage to an inductor, current flows, but it does not 'start' to flow after the voltage is applied, it starts immediately. But even if we look at it as 'after' then what about the capacitor.
If we "apply" a voltage to a capacitor, we get infinite current flow even with a tiny capacitance. Now we could say that you have to apply a current 'first' in order to charge the capacitor to some voltage, so that the voltage comes 'after' the current. But that' also not right, they both occur simultaneously.
Now we might go as far as to say that the "electric field" is 'first' established in a wire before current can flow. But in that view we are talking about *relative* values of current and electric field. In this case we deem a current as low as 1 femtoampere (for example) to be zero current when really it is not zero. Again it has to be simultaneous. Also we can look at how that electric field got established in the first place.
So the bottom line is that current and voltage are independent only in theory and we decide what theory we want to use.
It's ok to disagree with this but then you should have at least one physical example that demonstrates the contrary.