If current is just the movement of charged particles, why do the all have to move in the same direction?
For example, if you reverse-bias a diode (connect the positive terminal to the n-type side and the negative terminal to the p-type side), the positive "holes" are attracted to the negative terminal and the electrons are attracted to the positive terminal.
Firstly, if positive holes moving towards the negative terminal corresponds to electrons moving the opposite way (since "holes" aren't real, they're just a lack of electrons). So on both sides of the diode, electrons are moving in the same direction. I don't quite understand how this doesn't correspond to a current flowing.
Not even looking that deep into it, if positive charges are moving one way and negative charges the other, why does it matter if they cross the PN junction? Moving charges = electricity, right?
On top of all this, the battery creates an electric field that goes through all the wires, so why is there no current in the circuit? Electrons don't even move that fast (I've heard drift speed is on the order of cm/s), so "current" is localized in the sense that an electron on one side of a circuit may never even reach the other side. So why aren't localized electric fields enough to create a circuit?
Best Answer
The battery supplies a part of its chemical energy to the electrons that emerge out of it. These energized electrons lose this energy in the outer circuit, when they go through various electronic components. The electrons in a simple conductor collide due to their thermal energy.
Electrons move from the -ve terminal of the battery to the +ve terminal. In a reverse-biased diode, the electrons move from minority region (the p side) to the majority region (the n side) due to the electric field inside the diode which forces the charges from their minority region into their majority region.
Current is defined as the number of charges passing unit area of conductor per sec. The electrons inside a conductor without a battery, suffer a lot of collisions but their velocity on an average can be considered $0$ and hence, they are unable to produce current.
But when a battery is joined across the conductor an electric field is set up in it. Even in the presence of this electric field, the free electrons suffer a lot of collisions but now their movement gets a certain direction. The real motion is still zig-zag but with a certain direction. The high number of collisions are responsible for their slow drift speed.
As the electric field starts to accelerate the electron, the electron collides and loses its kinetic energy in form of heat. Then the field accelerates the electron again but the electron again collides and this goes on.
The electrons drift through the conductor and their speed ,in presence of E.field, is called drift speed. Although the drift speed of electrons is very low $( −0.000023 m/s)$ a large current is produced because of their high quantity crossing per unit area of the conductor per sec, which is about $10^{23}$ electrons.