Electrons that are loosely bound to the parent shell gain to some level of thermal energy from the surrounding
medium, cause the electrons to be removed from their orbit. When atoms lose their free electrons, they acquire a net positive
charge and are referred to as positive ions. The free electrons are
able to move within these positive ions and leave the general area of
the parent atom, while the positive ions only oscillate in a mean fixed
position. For this reason, the free electron is the charge carrier in a solid conductor of electricity.
What is electric current?
An electric current is a flow of electric charge in a circuit. More specifically, the electric current is the rate of charge flow past a given point in an electric circuit. The charge can be negatively charged electrons or positive charge carriers including protons, positive ions or holes.
The magnitude of the electric current is measured in coulombs per second, the common unit for this being the Ampere or amp which is designated by the letter 'A'. Current flow in a circuit is normally designated by the letter 'I', and this letter is used in equations like Ohms law where $V=IR$.
How electric current is produced?
Electric current is produced by making free electrons in motion by applying external force or energy. Free electrons exist naturally in some metals e.g copper, aluminum, iron, steel, etc. The external force may be applied by a battery or moving magnetic field or sunlight in the case of solar panels. The battery does its job by creating a deficiency of electrons in one metal through chemical reaction making it positive in nature when the metal is allowed to be in contact with another metal having free electrons, the free electrons start moving from high to low level (as like water goes from high to low level) to make both the metals of balanced charges. As the electrons start movement, the moment it is called current flow in the circuit. when there is no charge flow, there is no current flow in the action. On the other hand, there are other natural phenomena of moving a magnetic field which creates current flow in a wire when placed in its force of action. In the case of a hydroelectric dam, it's flowing water that's used as the power source to turn the turbine. The high speed of flowing water turns the turbine, which turns a metal shaft connected an electric generator, which is basically a motor that produces an electric current.