When the voltage is increased does the speed of electrons increase or does the electron density increase? I am just a high school student trying to self study, please excuse me if this question sounds silly to you.
I know that current is a product of the speed of electrons and the electron density.When current is increased it either means that the speed of electrons has increased or it means that the number density of the flowing electrons has increased.
I also know that voltage is directly proportional to current and when voltage increases(without no change in the resistance) the current will also increase.
But my question is, when voltage increases does an increase in the speed of electrons contribute for an increase in current or does an increase in electron density contribute for it.
If it isn't that black and white, then in what proportion will each of the two components increase? Does it randomly increase?
Related question:Say the electron density of a circuit that lights a light bulb increases.When this happens what change will we see in the brightness of the light bulb?I know that when the speed of electrons increase the brightness increases but what will happen when the electron density increases?
 A: In a conductive material such as a metal, for all practical purposes, current depends only on the speed of the electrons.  The electron density does not change because each metal atom has already given up all of its valence electrons; releasing further electrons would require a very large energy input.
In an insulator or semiconductor, the density of charge carriers may increase during electrical breakdown.  This occurs in avalanche diodes, neon lights, lightning bolts, and elsewhere.
A: Current is the amount of charge (electrons) passing a point in a wire per unit time. Voltage is the amount of energy in joule in every charge of 1 coulomb moving through the wire. Increase in current translates to increase in speed of electrons moving past our reference point. Electron density in a wire remain relatively constant even at high wire temperature. 
A: Increasing the voltage applied to a circuit of a given resistance will increase the current flow. That flow is defined in electrons per second past a point. So increasing the voltage increases the speed of the electron flow.
The number of electrons free to flow is a constant for a material.
For Copper that is one electron per atom.
