### Re: Can an external electric field create current?

Date: Sun Aug 17 14:39:19 2003
Posted By: Lawrence Skarin, Rochester Museum and Science Center Technical Assistance Group
Area of science: Physics
ID: 1059111859.Ph
Message:
```
We have to keep clear macroscopic stuff (like electric circuits, where
microscopic stuff works together so you can look at anything that happens
in a simple way).  For example, the current in a cylinder of copper is the
result of an electric field acting on electrons free to move in this
field.  99.99 percent of the time, this field is the result of a single
externally applied voltage.

The "current" is the result of a "current density" at any point in the
cross-section added up (in calculus, we call this "integration") over the
total cross-section area.  The current density is caused at every
microscopic point by the electric field acting on a mobile electron.
Because the current density across the cross-section is constant, we just
multply by the cross-section area to get current in amperes.  Then we say
the voltage across the whole cylinder times the current through the whole
cylinder equals the power dissipated in the cylinder.

Introducing another electric field complicates everything.  Here's my
recommendation.  Try to learn how a solar battery works.  This device uses
phenomena you suggest might be there.  A solar battery has a PN junction
which automatically creates an electric field external to all outside
influences.  Light particles (photons) landing on the junction create
charge carriers that are moved by the electric field out of the junction.

Try    http://science.howstuffworks.com/solar-cell.htm -- the wonderful
site that

```

Current Queue | Current Queue for Physics | Physics archives