Voltage, Current, and Resistance:Part 2
Current (Symbol: I)
- Electric current is the flow of electric charge in a conductor, such as a wire. It is a fundamental concept in electricity and is measured in units called amperes (A). Electric current can be either direct current (DC), where the flow of charge is in one direction, or alternating current (AC), where the flow of charge periodically reverses direction.
- In mathematical terms, electric current (I) is defined as the rate of flow of electric charge (Q) through a conductor over time (t). The relationship is expressed by the formula:
I=Q/t
where:
I is the electric current in amperes (A),
Q is the electric charge in coulombs (C),
t is the time in seconds (s).
Ampere:
Ampere, abbreviated as “A” or sometimes “Amp” is the base unit of electric current in the International System of Units (SI). It is defined as the amount of electric current that flows through a conductor in one second when one coulomb of electric charge passes through the conductor.
- In other words, one ampere is equivalent to one coulomb per second.
Mathematically, it can be expressed as:
1 ampere = 1 coulomb / 1 second
A current of 1 ampere means that there is 1 coulomb of charge passing through a cross section of a wire every 1 second.
- The currents are usually expressed in
| Teraamperes | 1 TA = 1012 A |
| Gigaamperes | 1 GA = 109 A |
| Megaamperes | 1 MA = 106 A |
| Kiloampere | 1 kA = 103 A |
| Milliamperes | 1 mA = 10-3 A |
| Microamperes | 1 µA = 10-6 A |
| Nanoamperes | 1 nA = 10-9 A |
| Picoamperes | 1 pA = 10-12 A |
| Femtoamperes | 1 fA = 10-15 A |
- Materials can be classified into conductors, insulators, and semiconductors based on their ability to conduct electric current.
a) Conductors –
Definition: A conductor is a material or substance that allows the flow of electric current. In other words, conductors have a high electrical conductivity, meaning they permit the movement of electric charge, typically in the form of electrons. Conductors are characterized by having a large number of free electrons that are not tightly bound to atoms and can move easily in response to an applied electric field.
Examples: Metals like copper, aluminum, silver, and gold are excellent conductors of electricity. In general, materials with a high density of free electrons tend to be good conductors.
b) Insulators –
Definition: Insulators are materials that do not allow electric current to flow easily through them. These materials have high electrical resistivity, which means they impede the movement of electric charge, typically in the form of electrons. In insulators, electrons are tightly bound to atoms, and they do not move freely in response to an applied electric field.
Examples: Rubber, glass, plastic, and wood are common insulators. Insulating materials typically have few free electrons, making it difficult for electric charge to move through them.
c) Semiconductors –
Definition: A semiconductor is a material that exhibits electrical conductivity between that of a conductor and an insulator. Semiconductors have properties that allow them to be selectively conductive or insulating, depending on external factors like temperature, the presence of impurities, or an applied electric field.
Examples: Common semiconductor materials include silicon, germanium, and compound semiconductors like gallium arsenide.
Differentiate between Conventional Current flow and Electron Flow
- In a circuit, electric current is typically carried by electrons in conductive materials like metals.
- The direction of conventional current flow is considered to be from the positive (+) to the negative (-) terminal, even though electrons actually move in the opposite direction.
| Features | Conventional Current Flow | Electron Flow |
|---|---|---|
| Direction | Positive terminal to negative terminal | Negative terminal to positive terminal |
| Charge carriers | Assumes positive charges are moving | Recognizes movement of negatively charged electrons |
| Historical basis | Established before electron discovery | Reflects actual movement of charge carriers |
| Usefulness | Widely used in circuit analysis and calculations | Increasingly popular in textbooks and advanced studies |
| Visual model | Easier to visualize with positive charges | Aligns with attraction of opposite charges |
| Impact on circuit behavior | No impact, similar predictions to electron flow | No impact, consistent with conventional current model |