→If an electric field is applied to conductor, an electric charge inside the conductor will experience a force. If electric charges are free to move then they constitute an electric current.
→ In nature such free electric charges are located in the upper layer of atmosphere called the ionosphere.
→In atoms and molecules, the electrons and the positively charged nuclei are bound to each other by electric force so, electrons are not free to move.
→Electrons are bound in some objects, so they do not accelerate even when an electric field is applied.
→In metals, the electrons are free to move within the material; but the motion of electrons is random. Due to this random motion no electric current is observed.
→When an external electric field is applied to them, á force is exerted on electrons, so all of them move in one direction which will create an electric current.
→In solid conductors, the current is carried by free electrons. where as in electrolytic solution both positive and negative ions develop electric current.
→In gases, the current is carried by ions, while in semi conductors free electrons and holes create electric current.