What is an electric current?
To understand what an electrical current is, you have to understand a little bit about the atom. Check out All About Atoms. Anyway, in a nutshell, atoms are split into two parts. The first is the nucleus that contains protons and sometimes neutrons. Orbiting around the nucleus are electrons. Usually there are the same number of electrons as there are protons. Now protons really determine what a material is, but electrons are where the action is. Almost all of what we interact with and things like chemistry happen at the level of the electrons. What most people don't realize is that electrons are very mobile. Many atoms actually hook up and share electrons! The same electron might live on two different atoms. Electrons can come loose and move between atoms. The ease at which electrons move is dependent on what atoms they come from. In some materials, which we call conductors, electrons move very easily. An electric current is electrons moving through a material, by jumping from atom to atom. When an electron jumps off one atom it leaves a hole for the next electron to jump into and so on down the line. Wouldn't it be pretty cool to have eyes so powerful to see stuff like that? Unfortunately no one does, so we have to try to understand it by the observing the effects they cause. We try to make good guesses about how something happens and then try experiments to prove or disprove what we guessed.
Brian Kross, Chief Detector Engineer (Other answers by Brian Kross)