# Electric currents

1. Dec 27, 2008

### cam875

Out of curiousity is it possible to generate a split second of an electrical current which would be more of an electrical signal by literally boucing an electrical conductor off of another electrical conductor, such as copper hitting copper sending the electrons flying down the current or would this take too much energy or something.

2. Dec 27, 2008

### Burningmace

Firstly, electrons don't operate with usual Newtonian mechanics. But even if they did, you have to think about how momentum works. Momentum is mass multiplied by velocity (p=mv). If you have an electron moving at 1000m/s, it still only has a mass of about 9.1x10^-31 kg, so its momentum is only 9.1x10^-28 kg·m/s.
Momentum and force are related by time (F=p/t). The force exerted would be tiny, even if the time taken to slow from 1000m/s to 0m/s was 0.1 milliseconds, you're looking at a force of 9.1x10^-28 Newtons. The attraction force (Coulomb's law) says that F=(q1·q2)/(4pi·E0·(r^2)), where E0 is the permittivity of space. Using the Bohr radius (5.291x10^-11 m) and the electron/proton charges (1.609x10^-19 C, negative for electrons) we can calculate that the attractive force between the electron and nucleus of a Hydrogen atom is around 8.3x10^-8 N, which is tens of orders of magnitude higher than the force of deceleration we calculated above.

In short, we can basically say that the force of electrical attraction between the nucleus and electrons in an atom is much much greater than any force you can reasonably generate from hitting two pieces of copper together.

3. Dec 28, 2008

### cam875

ok cool makes sense so now im going to ask how does a battery start an electrical current. thanks in advance and for the good answer above.

4. Dec 28, 2008

### Burningmace

A battery works with a chemical reaction, performing what is basically the opposite of electrolysis. Salts and metals react to produce ions. The electrons flow freely between each "half cell" of the battery. When there is no circuit, the electrons have nowhere to go and don't pass between the cells. When there is a circuit, the electrons flow producing an electric current.