What is Electric Current?

Electric current is the flow of electric charge. It refers to the flow of electrons in a conductor such as a metal wire. Electric charge flows when there is a voltage difference between two points in a circuit, creating an electric field that causes electrons to move.

Current is measured in amperes or “amps” for short. An ampere defines the amount of electric charge flowing past a point in the circuit over time. For example, one ampere means one coulomb of charge (around 6.24 x 10^18 electrons) flows past a point per second.

The amount of current flowing in a circuit depends on the voltage supplied and the resistance in the circuit. A higher voltage can create a stronger electric field in a conductor, leading to more current flow. Resistance opposes current flow, meaning that higher resistance reduces the amount of current for a given voltage.

Electric Charge

Electric charge is a fundamental property of subatomic particles that is quantized, meaning it comes in discrete units. Some particles like protons have positive electric charge, while others like electrons have negative charge. The magnitude of electric charge is measured in units called coulombs (represented by the symbol C). The protons in an atom have a charge of +1 C, while electrons have a charge of -1 C.

When an object has an equal number of protons and electrons, its positive and negative charges balance out, resulting in a net charge of zero. But when the charges are unequal, an object acquires a net charge that is either positive or negative depending on which particles dominate. Charged particles interact with each other through the electromagnetic force and exhibit attractive and repulsive behaviors.

Flow of Charge

Electric current is a flow of electric charge. A current is produced when there is a difference in electric potential between two points, caused by an electric field. Charge will flow from a region of higher potential to lower potential. Electrons in a conductor will move towards the more positive potential, while positive charges move towards more negative potential.

The flow of electric current is often compared to the flow of water in a pipe, or the flow of vehicles in traffic. As with water or traffic flow, the electric current flows predictably in the path of least resistance. Metallic wires provide an easy path for charges to flow, just as a highway allows cars to flow smoothly compared to side roads. And similar to varying the diameter of a pipe or width of a road to increase flow, increasing the cross-sectional area of a wire will allow more charges to flow.

By convention, the direction of electric current flow is taken as the direction positive charges would flow. So in a metal wire, electric current flows from the positive to the negative terminal, even though the charge carriers are electrons moving the opposite direction.

Measuring Current

Current is measured in the unit of Ampere or amps, represented by the symbol A. When electric charges flow, the rate at which they flow is measured in amps. Ampere is the basic unit of current measurement in any electric circuit.

Ammeter is the instrument used to measure the amount of electric current flowing in a circuit. It is connected in series in a circuit to measure the current flowing through it. When current flows through an ammeter, it deflects the pointer indicating the magnitude of the current in amperes.

The larger the amount of charge flowing through a circuit per unit time, the larger is the current. Using an ammeter helps us determine the rate of flow of charge which is the electric current.

Ohm’s Law

An important concept in understanding electric current is Ohm’s law. This law, named after German physicist Georg Simon Ohm, states that there is a consistent link between the voltage of electric current, the resistance in a circuit, and how much current flows through the circuit. The mathematical equation summarizes this relationship:

Current (I) = Voltage (V) / Resistance (R)

What this equation shows is that the electrical current that moves through wires or other conductors is proportional to the voltage applied across the circuit. For example, if the voltage is doubled, the current through that same conductor also doubles, assuming the resistance remains constant.

Conversely, if the resistance in the circuit increases, less current will flow for the same applied voltage. Using Ohm’s Law allows calculations of current, voltage or resistance when any two of those values are known. This fundamental relationship is key to analyzing any electrical circuit.

Direct Current vs. Alternating Current

Direct current (DC) and alternating current (AC) are the two types of electric current we use in modern applications. They differ in how they flow and change direction:

Direct Current

Direct current refers to the constant flow of charged particles in a single direction. In a DC circuit, electrons flow from the negative to positive terminal. The voltage and current are constant over time.

Alternating Current

Alternating current means the flow of electric charge periodically changes direction. In an AC circuit, the current flows back and forth due to the alternating voltage. So the direction of the flow of charge is constantly switching positive to negative and back again.

In AC power systems, the frequency at which the current switches direction is measured in cycles per second or hertz (Hz). Common electric systems use 60 Hz frequency meaning the AC current switches directions 120 times per second (60 Hz = 60 cycles per second).

DC Current Applications

Direct current (DC) is useful for electrical devices that require a constant flow of electrons in one direction only. Some common DC current applications include:

Batteries – Batteries come in many shapes and sizes to supply DC power to portable electronics like vehicles, flashlights, toys, and laptop computers. Alkaline batteries contain chemicals that react and produce a DC flow of electrons from the negative to positive terminals.

Solar Cells – Solar photovoltaic panels directly convert sunlight into DC electrical energy using the photovoltaic effect. The solar cells are made of semiconductor materials like silicon that contain electric fields which drive electrons when exposed to photons.

Fuel Cells – Fuel cells generate DC current via an electrochemical process fueled by hydrogen gas. Like a battery, they contain a positive and negative terminal connected by an electrolyte. Fuel cell technology is used to power a range of devices from vehicles and boats to smartphone battery packs.

LEDs – Light emitting diodes or LEDs operate on DC current, with electrons flowing smoothly through the semiconductor to produce light. LEDs find widespread usage for efficient lighting, displays, decorations, signage, TVs/monitors, and other electronics.

AC Current Applications

AC current has several key applications in modern society:

Power Grid and Wall Outlets

The electricity that comes from power plants to homes and businesses is AC current. The standard wall outlets in most countries operate at 120 or 220-240 volts AC. This allows compatible devices to be plugged in to power appliances, lights, computers and more.

Motors & Transformers

The alternating nature of AC current allows for the electromagnetic induction that is key to the operation of motors and transformers. Motors convert electrical energy into mechanical energy to drive pumps, fans, conveyor belts and more. Transformers can step voltages up or down easily using AC power, enabling long distance transmission along power lines.

Effects of Electric Current

Electric current has several important effects that are utilized in many practical applications. The two main effects of electric current are heating and magnetic effects.

Heating Effect

Electric current passing through a conductor produces heat. This effect occurs due to resistance of the material to the flow of electrons. The collisions between the moving electrons and the atoms of the conductor convert the kinetic energy of electrons into heat energy. Higher the current flow, greater is the heating in the conductor. The amount of heat produced depends on:

• The amount of current flowing through the conductor
• The resistance per unit length of the conductor
• The time duration for which the current flows

The Joule heating effect of electric current has many practical applications like electric kettles, irons, electric heaters, electric welding, and more.

Magnetic Effect

When electric current passes through a conductor, it produces a magnetic field surrounding the conductor. This is called the magnetic effect of the electric current. The strength of the magnetic field depends on:

• The amount of current flowing through the conductor
• The shape and size of the conductor loop

This magnetic effect of current has many applications. Electromagnets, electric motors, generators, solenoids, inducers all utilize this magnetic effect of the electric current.

Safety

Electric currents can pose serious risks if not handled properly. While current flows through many devices we use safely every day, exceeding current ratings or failing to take adequate precautions can lead to electric shocks, fires, or damage to property.

Current Rating and Safety Limits

Every circuit or device has a rated maximum amount of current it can safely handle. Exceeding this could overheat wires or components, posing fire risks and other dangers. Reputable manufacturers design their products not to exceed safe current limits during normal operation. But device malfunctions, damaged or improperly installed wiring, or user modifications could still cause excessive current flow. So it’s always important to use devices only as intended within manufacturer ratings.

Grounding, Circuit Breakers, and GFCIs

Several safety mechanisms help prevent excessive current and shock hazards:

• Proper electrical system grounding provides a safe path for current flows due to faults or malfunctions.
• Circuit breakers automatically open circuits with sustained over-currents before dangerous conditions occur.
• GFCIs (ground fault circuit interrupters) quickly break circuits with leakage current flows, protecting users from severe shocks.

Using GFCI outlets in kitchens, bathrooms and other areas with higher risk of electric shock is especially advisable. Maintaining electrical systems according to local building codes also helps minimize risks from electric current.