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In the scientific model, electric current is the overall movement of charged particles in one direction. The cause of this movement is an energy source like a battery, which pushes the charged particles. The charged particles can move only when there is a complete conducting pathway (called a ‘circuit’ or ‘loop’) from one terminal of the battery to the other.
A simple electric circuit can consist of a battery (or other energy source), a light bulb (or other device that uses energy), and conducting wires that connect the two terminals of the battery to the two ends of the light bulb. In the scientific model for this kind of simple circuit, the moving charged particles, which are already present in the wires and in the light bulb filament, are electrons.
Electrons are negatively charged. The battery pushes the electrons in the circuit away from its negative terminal and pulls them towards the positive terminal (see the focus idea Electrostatics – a non contact force). Any individual electron only moves a short distance. (These ideas are further elaborated in the focus idea Making sense of voltage). While the actual direction of the electron movement is from the negative to the positive terminals of the battery, for historical reasons it is usual to describe the direction of the current as being from the positive to the negative terminal (the so-called ‘conventional current’).
The energy of a battery is stored as chemical energy (see the focus idea Energy transformations). When it is connected to a complete circuit, electrons move and energy is transferred from the battery to the components of the circuit. Most energy is transferred to the light globe (or other energy user) where it is transformed to heat and light or some other form of energy (such as sound in iPods). A very small amount is transformed into heat in the connecting wires.
The voltage of a battery tells us how much energy it provides to the circuit components. It also tells us something about how hard a battery pushes the electrons in a circuit: the greater the voltage, the greater is the push (see the focus idea Using energy).
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