Electric Current

Electric Current

Electric current is the flow of electric charge through a material. It is the rate at which electric charge flows past a point in a circuit. The flow of electric charge is typically carried by electrons, which are negatively charged particles.

The SI unit for current is the coulomb per second, or the ampere (A), which is an SI base unit: 

1 ampere = 1A = 1 coulomb per second = 1 C/s.

An instrument used to measure currents is called an ammeter. To measure the current in a wire, you usually have to break or cut the wire and insert the ammeter so that the current to be measured passes through the meter. An ammeter always measures the current passing through it. An ideal ammeter would have zero resistance, so including it in a branch of a circuit would not affect the current in that branch. Real ammeters always have some finite resistance, but it is always desirable for an ammeter to have as little resistance as possible.

Electric current is essential for the operation of electrical devices and systems. It allows for the transfer of electrical energy from a power source to a load, which can then be converted into other forms of energy, such as heat, light, or motion. Understanding the properties of electric current is important in the design and analysis of electrical circuits and systems.

Electric currents create magnetic fields, which are used in motors, generators, inductors, and transformers. In ordinary conductors, they cause Joule heating, which creates light in incandescent light bulbs. Time-varying currents emit electromagnetic waves, which are used in telecommunications to broadcast information.

Types of Electric Current

There are three types of electric current:

1. Direct Current (DC): A flow of electric charge that flows in one direction is called direct current. The magnitude and direction of DC remains constant over time.
2. Alternating Current (AC): Alternating current is the flow of electric charge that changes direction periodically. The magnitude and direction of AC varies with time, usually in a sinusoidal pattern.
3. Pulsed DC: Pulsed DC is a type of current that flows in pulses or brief bursts. The pulses may be unidirectional or bidirectional, but they are not continuous like DC or AC currents. This type of current is often used in specialized applications such as welding and electroplating.

How does electric current flow – Mechanisms of the current flow

In electrostatic situations, the electric field is zero everywhere within the conductor, and there is no current. However, this does not mean that all charges within the conductor are at rest. In an ordinary metal such as copper or alumium, some of the electrons are free to move within the conducting material. These free electrons move randomly in all directions, somewhat like the molecules of a gas but with much greater speeds, of the order of 10⁶ m/s. The electrons nonetheless do not escape from the conducting material, because they are attracted to the positive ions of the material. The motion of the electrons is random, so there is no net flow of charge in any direction and hence no current.

When a voltage difference is applied across a conductor, it creates an electric field within the material. The electric field exerts a force on the free electrons within the conductor, causing them to move from areas of high potential energy to areas of lower potential energy. The flow of electrons in response to the applied electric field is what we refer to as an electric current.

In conductors, the valence electrons are essentially free and strongly repel each other. Any external influence which moves one of them will cause a repulsion of other electrons, which propagates “domino fashion” through the conductor.

Application of Electric Current

Electric current has numerous applications in various fields. Some of the major applications of electric current are:

1. Power generation and distribution: Electric current is used to generate, transmit, and distribute electrical power to homes, businesses, and industries.
2. Lighting: Electric current is used to power various types of lighting systems, including incandescent bulbs, fluorescent lamps, LED lights, and others.
3. Heating and cooling: Electric current is used to heat and cool homes and buildings using devices such as heaters, air conditioners, and refrigerators.
4. Electronics: Electric current is used to power electronic devices such as computers, televisions, radios, and mobile phones.
5. Transportation: Electric current is used to power electric vehicles, trains, and other forms of public transportation.
6. Medical applications: Electric current is used in various medical devices and treatments, such as electrocardiograms (ECGs), electroencephalograms (EEGs), and nerve stimulation therapies.
7. Manufacturing: Electric current is used in various manufacturing processes, such as welding, electroplating, and electrolysis.
8. Communication: Electric current is used to power various communication systems, such as telephones, telegraphs, and internet networks.

These are just a few examples of the many applications of electric current. Understanding the principles of electric current is important for a wide range of industries and fields.

Electron Current in Nature

Electric current is a natural phenomenon that can be found in a variety of forms in the natural world. Here are some examples of electric current in nature:

1. Lightning: Lightning is a powerful discharge of electric current that occurs during a thunderstorm. It is caused by the buildup of electrical charges in the atmosphere, which are discharged as a lightning bolt.
2. Electric eels: Electric eels are fish that can generate electric currents of up to 600 volts. These electric currents are used by the eels to stun their prey and for navigation in murky waters.
3. Electric rays: Electric rays are a type of fish that are capable of generating an electric current. They use this electric current to stun their prey and to defend themselves from predators.
4. Bioelectricity: Many living organisms, including humans, generate electric currents as part of their normal biological processes. For example, the human heart generates an electrical signal that is responsible for regulating the heartbeat.
5. Geoelectricity: Geoelectricity refers to the natural electric currents that exist within the Earth’s crust. These currents are caused by the movement of charged particles in the ionosphere and the magnetosphere.
6. Volcanic lightning: Volcanic lightning is a rare phenomenon that occurs during a volcanic eruption. It is caused by the buildup of electrical charges in the volcanic plume, which are discharged as a lightning bolt.

Examples of Electric Currents in Amperes

Here are ten examples of electric currents in amperes, sorted from smallest to largest:

1. The current required to light up an LED (Light Emitting Diode) is typically between 10-20 milliamperes (mA).
2. The charging current of a small USB-powered device, such as a smartphone, is typically around 1 ampere (A).
3. The current flowing through a household light bulb when it is turned on is typically between 0.1 and 1 A.
4. The current flowing through a typical laptop charger is around 2-3 A.
5. The current required to start a car engine is typically around 50-100 A.
6. The current flowing through a household electric stove when all of its heating elements are turned on can range from 20 to 50 A.
7. The current flowing through a high-speed train can range from 1,000 to 3,000 A.
8. The current flowing through a typical electric car charging station can range from 20 to 400 A, depending on the charging rate.
9. The current required to power a small electric motor, such as the ones used in power tools or household appliances, can range from a few amperes to several hundred amperes.
10. The current flowing through a typical industrial welding machine can range from 50 to 500 A.

Electric Current and Hydraulic Analogy

The hydraulic analogy, or the electric-fluid analogy, is a widely used analogy between hydraulics and electricity, which is a useful tool for teaching and for those who are struggling to understand how circuits work. it can also be applied to heat transfer problems. 

Current is equivalent to a hydraulic volume flow rate; that is, the volumetric quantity of flowing water over time. Usually measured in amperes. The wider pipe is, the more water will flow through. It is measured in amps (I or A).

Resistance is like pipe diameter or obstacles in the hose that slow down the water flow. It is measured in ohms (Ω). In hydraulics, resistance is associated with the pressure loss coefficient.