CURRENT

Whenever there is movement of charge carriers in a substance, there is an electric current. Current is measured in terms of the number of charge carriers, or particles containing a unit electric charge, passing a single point in 1 second.
Charge carriers come in two main forms: electrons, which have a unit negative charge, and holes, which are electron absences within atoms and which carry a unit positive charge. Ions can act as charge carriers, and in some cases, atomic nuclei can too. These types of particles carry wholenumber multiples of a unit electric charge. Ions can be positive or negative in polarity, but atomic nuclei are always positive.
Usually, a great many charge carriers go past any given point in 1 second, even if the current is small. In a household electric circuit, a 100-W light bulb draws a current of about 6 quintillion (6 × 10¹⁸) charge carriers per second. Even the smallest minibulb carries a huge number of charge carriers every second. It is ridiculous to speak of a current in terms of charge carriers per second, so usually it is measured in coulombs per second instead. A coulomb (symbolized C) is equal to approximately 6.24 ×10¹⁸ electrons or holes. A current of 1 coulomb per second (1 C/s) is called an ampere (symbolized A), and this is the standard unit of electric current.
A 60-W bulb in a common table lamp draws about 0.5 A of current. When a current flows through a resistance—and this is always the case, because even the best conductors have resistance—heat is generated. Sometimes visible light and other forms of energy are emitted as well. A light bulb is deliberately designed so that the resistance causes visible light to be generated. However, even the best incandescent lamp is inefficient, creating more heat than light energy. Fluorescent lamps are better; they produce more light for a given amount of current. To put this another way, they need less current to give off a certain amount of light.
In physics, electric current is theoretically considered to flow from the positive to the negative pole. This is known as conventional current. If you connect a light bulb to a battery, therefore, the conventional current flows out of the positive terminal and into the negative terminal. However, the electrons, which are the primary type of charge carrier in the wire and the bulb, flow in the opposite direction, from negative to positive. This is the way engineers usually think about current.