This is the start of my resource but I thought it fitting to post as a reply to this thread.
The world of Physics, shall we say can get a bit confusing at times, that’s probably an understatement. There are so many different opinions on what actually happens regarding current, energy, electric fields, magnetic fields and charge within a conductor.
Understanding the ins and outs of this is not necessary needed if only a basic understanding of electronic components, and conductors is needed. In most cases that is all that is needed. Many great designs exist without the designer needing to go into the physics of component operation and what happening in the wires down at the microscopic level.
I mean we can produce very reliable, complex designs without even realising that we are working the wrong way round to what actually happens. But we have crafted the skills over time to allow us to ignore this and still understand how to design circuits that actually operate in reverse to what we think.
What I am talking about is electrical current and it’s direction, when Ben Franklin made the decision on the direction he had a 50-50 chance of getting it right. Well he got it wrong. But by the time we worked all this out it was too late to do much about it so we invented the terms conventional current direction and actual current direction. Strange isn’t it?
We can even work out how to control components like BJTs even by using the incorrect terminology i.e. we say current control and not voltage control. How? Because all the physical properties of components have something in common, and that’s resistance, inductance and capacitance and the mixture of all these called impedance.
Every component has a total impedance it just depends on the percentage concentration of mixture of the three elements which determines what the component is and its uses. This is what makes a capacitor inductor and resistor different. So when we apply a voltage across a resistor for example we will produce a current in that component.
This current will produce a voltage difference between the two terminals of the resistor. So if we increase the applied voltage then the current will increase because of the increase in voltage between the two terminals of the component. So this makes sense because of the linked relationship between current voltage and resistance (Ohms Law) we can increase the voltage and have an increase in current but we can also reduce the resistance and have an increase in current also.
So if we take the BJT example in figure 1 because it is perfect for explaining how incorrect statements can still be used to predict reliably component behaviour.
Figure 1 BJT NPN collector/emitter current control example.
Three engineers are asked to modify the circuit in a way as to vary the current in R1. Then asked to explain the operation of what they have done. They are all told they can’t change the applied voltage, that is fixed and also the value of R1 itself is fixed. So they all say well that’s easy we need to adjust the value of P1 and because it’s a variable resistor we just turn it in either direction to vary the resistance. This will increase or decrease the current.
Engineer 1 says “ I confirm that I have reduced the base resistance of P1 to increase the collector current. So I confirm that this resistor change is controlling the collector current”
Engineer 2 says “ I confirm that I have reduced the base resistance of P1 to increase the collector current. So I confirm that the increase in current in P1 as a result from changing the value of P1 is controlling the collector current”
Engineer 3 says “ I confirm that I have reduced the resistance of P1 to increase the collector current. So I confirm that the increase in current in P1 results in a lower voltage drop across P1 as a result from changing the value of P1 which in turn increases the voltage at the base of P1 ”
Now only one of these is technically correct. All three methods used by the engineer is the same, changing the value of P1. But three different explanations.
Engineer 1 is only concerned with the changing value of P1 he is not concerned about the current or voltage. Engineer 2 is only concerned about current and nothing else. Engineer 3 is only concerned about the base voltage and knows that if this changes then the collector current will change.
But the one thing they all have in common is they all knew that by adjusting the value of P1 this would adjust the collector current. This is how we have accumulated so many different reasoning in electronics, but only one can be absolutely correct. But does it really matter as long as the results are the same, no not really. Unless to are teaching someone the correct way all this works then do what ever works for you.