Current Electricity Fundamentals

Current Electricity

In the senior secondary school curriculum, students delve into modern physical sciences, including physics, which covers various aspects of classical mechanics, thermodynamics, sound, light, heat transfer, chemistry, nuclear physics, atomic structure, electronics, geophysics and astronomy among others. Within the realm of physics, one significant unit focuses on electric fields and forces, capacitance, resistivity, and Ohm's law—all fundamental elements of current electricity.

Electric Current and Resistance

One of the primary topics within current electricity involves the direction of electric currents. An electric current consists of the movement of positive charges away from the positive side of the battery and negative charges towards the negative side. Inside materials like metals, there are free electrons that move around randomly; under the influence of an electrical field, these electrons start a slow drifting motion called electric drift. Direct current flows in only one direction, whereas alternating current changes direction periodically.

Ohm's law establishes a relationship between the current flowing through a circuit, the voltage across it, and the material properties of the components. According to Ohm's law, J=V/R, where J represents the current, V indicates the voltage, and R denotes the resistance of the substance. Resistance is the opposition offered by a substance to the passage of electric current. Resistivity is the property of a substance that determines how resistant it is to the passage of electric current. Resistivity is measured by the Greek letter rho (ρ) and gives a measure of how much resistance a substance has per unit length.

Power and Energy

Power is the rate at which work is done or energy is expended. Work done per unit time results in power. Meanwhile, energy is the capacity to do work. When the rate of doing work is constant, it produces power. The formulas relating power to work done, energy, and time are:

[P = \frac{W}{T}], where (P) is power, (W) is work done, and (T) is time elapsed during which the work is being done.

[E = PT]

where E is total energy, (P) is power, and T is time over which the power acts.

DC Circuits and Emf

Direct current (DC) passes through a closed circuit without reversal of current direction. Typical sources of direct current include batteries. The emf of a cell stands for electromotive force and represents the tendency of a source of electric power to produce a current in a complete circuit connected to its terminals. Cell voltages are usually given in volts, while the maximum available output of a cell is stated in milliamperes.

Understanding these basic tenets prepares students for further studies in electricity, electronics, and electricity supply, helping them grasp the foundational principles of electrical engineering.