Electric current is the flow of electric charge through a conductor, typically a metal like copper or aluminum. In most cases, the charge carriers responsible for the current are electrons. The movement of electrons through the conductor creates an electric current.
Electric current is quantified as the amount of charge passing through a conductor per unit of time, and it is measured in amperes (A).
Electrons are fundamental particles with a negative charge. In a conductor, such as a metal wire, electrons are loosely bound to the atoms and can move freely. When an electric field is applied, these free electrons begin to move, resulting in an electric current.
The movement of electrons in a conductor is called "drift" and occurs under the influence of an applied electric field. This drift results in a flow of electric charge, and this flow is what we observe as electric current.
In a typical metallic conductor, the electric field causes the free electrons to move toward the positive terminal of the voltage source, while the positive charges (ions in the metal lattice) remain stationary. This results in a net movement of negative charge (electrons), creating an electric current.
Mathematically, the number of electrons \( N \) passing through a conductor is related to the electric current \( I \) by the equation:
Where:
Since each electron carries a fundamental charge (\(e = 1.602 \times 10^{-19}\) C), the current can also be expressed in terms of the number of electrons moving through the conductor:
Where \( N \) is the number of electrons passing through the conductor in time \( t \).
The drift velocity \( v_d \) is the average velocity at which electrons move under the influence of an electric field. It is typically much smaller than the random thermal velocity of electrons, but it is responsible for the steady flow of current.
The relationship between drift velocity and current in a conductor can be written as:
Where:
The intensity of an electric current (how much charge flows per unit time) depends on several factors, including:
The voltage \( V \), also known as the potential difference, is the force that drives electrons to move through a conductor. The higher the voltage, the greater the current for a given resistance. This relationship is described by Ohm's Law:
Where:
Thus, increasing the voltage across a conductor increases the current, assuming resistance is constant.
The resistance \( R \) of a conductor depends on its material, length, and cross-sectional area. A longer conductor with a smaller cross-sectional area has higher resistance, reducing the flow of current. The relationship between resistance and the material properties is given by:
Where:
Thus, materials with high resistivity and long conductors increase the resistance and reduce the current.
The resistance of most materials increases with temperature. As the temperature rises, the atoms in the conductor vibrate more, obstructing the flow of electrons and increasing the resistance. This results in a decrease in the current for a given voltage.
A larger cross-sectional area provides more space for the electrons to flow, reducing the overall resistance and increasing the current. Conversely, a smaller area results in higher resistance and lower current.
In summary, electrons are the primary charge carriers responsible for electric current. The intensity of electric current is determined by several factors, including the voltage applied to the conductor, the resistance of the material, the length and area of the conductor, and the temperature. Understanding these factors is crucial in designing electrical systems and ensuring the efficient transfer of electrical energy.