Free electrons are necessary for electric current, but for those electrons to move, they need a complete pathway, or circuit, and there must be a force to make them move. The force from a battery sets free electrons moving.
Like charges repel, so the negative electrons are repelled from the negative terminal. Unlike charges attract, so the electrons are also attracted towards the positive terminal.
They flow in one direction only. This is called direct current or DC. Most circuits in motor vehicles use direct current.
The larger the charge at the positive terminal, the more strongly it attracts free electrons. This attraction acts as a force driving the electrons along. The greater the force, the stronger the electrical current. The force is called electromotive force or EMF. It’s also known as "voltage".
Also affecting the current flow in a circuit is electrical resistance, measured in ohms. All materials have resistance - even good conductors.
Four factors determine the level of resistance:
The higher the temperature, the harder it is for electrons to pass through it and the higher the resistance. While all materials have some resistance to current flow, a resistor is a component designed to cause a particular voltage drop in a circuit. It has a set resistance, usually marked or coded on its surface.
Since electric current is the flow of electrons, it's natural to say the direction of current is the direction in which electrons move. However, before the discovery that electric current was the flow of electrons, it was thought the natural way for electricity to move was from positive to negative.
Both concepts are still in use. Current said to flow from positive to negative, is called conventional current. Current said to flow from negative to positive, is called electron current.
