What is the difference between a transistor and a variable resistor?
A resistor is considered a passive device and has two connections and a nominal fixed resistor.
A transistor is considered an active device and has three connections.
A terminal is a control terminal, and when this terminal is controlled accordingly, it affects the apparent resistance between the other two. Hence the term “semiconductor”.
As a result, the resistance is subject to a fixed restriction on the current flow in the device, the amount depending on the fixed resistance value R.
The current that flows is = V / R.
In the transistor, the amount of restriction (by the base current of a BJT or the gate voltage of a MOSFET) can be modulated using the third terminal and therefore becomes an active control device. You can switch, amplify or modulate at high speed.
A resistor has a fixed resistance that does not change. It also has only two connections, an input and an output, the output depending on the input and the resistance.
A transistor is like a resistor, except that its resistance can be controlled by a second input called the base input.
In addition, the gate input of the transistor is the emitter and the output is the collector (for some reason also backwards).
When a negative current is applied to the base input, the resistance increases, which prevents current from flowing from the emitter to the collector and a transistor acting as a switch.
If a positive current is supplied to the base and a second negative current source is connected to the emitter, the input is amplified in proportion to the base current