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Illustration of the "reference directions" of the current (), voltage (), and power () variables used in the passive sign convention.If positive current is defined as flowing into the device terminal which is defined to be positive voltage, then positive power (big arrow) given by the equation = represents electric power flowing into the device, and negative power represents power flowing out.
A battery or galvanic cell in use has a cathode that is the positive terminal since that is where conventional current flows out of the device. This outward current is carried internally by positive ions moving from the electrolyte to the positive cathode (chemical energy is responsible for this "uphill" motion). It is continued externally by ...
In electronics, other forms of electric current include the flow of electrons through resistors or through the vacuum in a vacuum tube, the flow of ions inside a battery, and the flow of holes within metals and semiconductors. A biological example of current is the flow of ions in neurons and nerves, responsible for both thought and sensory ...
On many dry batteries, the positive terminal (cathode) is a protruding metal cap and the negative terminal (anode) is a flat metal disc (see Battery terminal). In a galvanic cell such as a common AA battery, electrons flow from the negative terminal to the positive terminal, while the conventional current is opposite to this. [6]
Therefore, the electrodes are named based on the direction of this "forward" current. In a diode the anode is the terminal through which current enters and the cathode is the terminal through which current leaves, when the diode is forward biased. The names of the electrodes do not change in cases where reverse current flows through the device.
Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current. [1]
When it is operating in the second or fourth quadrant, current is forced to flow through the device from the negative to the positive voltage terminal, against the opposing force of the electric field, so the electric charges are gaining potential energy. Thus the device is converting some other form of energy into electric energy.
Diagram of D'Arsonval/Weston type galvanometer. As the current flows from + terminal of the coil to − terminal, a magnetic field is generated in the coil.This field is counteracted by the permanent magnet and forces the coil to twist, moving the pointer, in relation to the field's strength caused by the flow of current.