✍️01-Basic Electricity

Learning electricity from the perspective of energy

What is Electricity

From the light that brightens our nights to the smartphones that keep people connected, electricity is an essential part of modern life. But what is it actually?

At its core, electricity is the flow of electrons.

Electrons are subatomic particles that orbit the nucleus of an atom. When these electrons move from one atom to another, they create a flow of electrical charge, akin to the way water flows in a river.

In most cases, these electrons traverse through conductive materials like metals—imagine copper wires in electrical circuits. The following image illustrates a row of atoms, with electrons passing from one to another like balls being tossed between people in a line.

Voltage, Ampere, and Ohm


Voltage, often referred to as electric potential difference, is one of the foundational concepts in the realm of electricity.

This term can be traced back to the renowned Italian physicist Alessandro Volta, who in the late 18th and early 19th centuries made groundbreaking contributions to the field of electricity. It's in his honor that the term "volt," the unit of voltage, is derived.

Physically, voltage represents the energy per unit charge. In simpler terms, it can be thought of as the "electrical pressure" or the force that drives electric current through a conductor. Because this difference that causes electrons to move, thereby creating current.

Mathematically, voltage is often represented by the letter 'V' and its standard unit is the 'volt' (symbol: V). Other commonly used units for voltage and their relationship to Volts are listed in Table 1. As one delves deeper into electrical engineering and physics, the importance of understanding voltage and its implications becomes paramount.

Table 1:


Relation to Volts (V)

Typical Scenarios


10⁻⁶ V

Bioelectrical signals, low-level sensor outputs


10⁻³ V

Audio signals, thermocouple outputs


1 V

Standard electronic circuits, batteries


10³ V

High voltage power lines, x-ray machines


10⁶ V

Ultra high voltage transmission lines, substations

Current and Ampere

The ampere, often shortened to amp, is the unit of electric current in the International System of Units (SI).

The term and the unit are named after André-Marie Ampère, a French physicist and mathematician who was one of the founders of the science of classical electromagnetism, often referred to as "electrodynamics."

In practical applications, current is what powers our devices. For instance, when you switch on a light bulb, it's the flow of current that illuminates it. Depending on the magnitude and requirements of devices, current can be described using multiple units, as listed in Table 2.

Table 2:


Relation to Amperes (A)

Typical Scenarios


10⁻⁹ A

Leakage currents, some types of sensors


10⁻⁶ A

Ultra-low power devices, quartz watch circuits


10⁻³ A

Consumer electronics, small electronic circuits


1 A

Appliances, regular electronic devices, charging currents


10³ A

Heavy industrial equipment, high capacity circuit breakers

Resistance and Ohm

Resistance is another fundamental concept in the study of electricity. Resistance can be analogized to the narrowness of a straw through which you're trying to sip a thick milkshake. The thinner the straw (higher resistance), the harder it is for the milkshake (current) to flow through, while a wider straw (lower resistance) allows the milkshake to flow more easily. Just as the diameter of the straw determines the ease of flow, resistance in a material governs how readily electric current can pass through it.

The unit for measuring resistance is "Ohm," symbolized by the Greek letter "Ω." The term honors the German physicist Georg Simon Ohm, who first formulated Ohm's Law. This foundational principle states that the current passing through a conductor between two points is directly proportional to the voltage across the two points when the temperature remains constant. We will delve deeper into Ohm’s Law in our Basic Electric Circuits course.

Different materials and components exhibit varying degrees of resistance. For instance, metals like copper and aluminum have low resistance and are commonly used as conductors, while rubber and glass have high resistance, making them effective insulators. Refer Table 3 for appropriate units. The resistance value of a material is also influenced by its physical dimensions, temperature, and other factors, this will be discovered tangibly in our Fundamental Thermoplastics course.



Relation to Ohms (Ω)

Typical Scenarios

10⁻³ Ω

Low resistance materials, shunt resistors for current measurement


1 Ω

General-purpose resistors, internal resistance of small devices

10³ Ω

Pull-up and pull-down resistors, many analog electronic circuits

10⁶ Ω

High resistance materials, insulation resistance, input impedance of some devices

High Voltage vs. Low Voltage

High voltage refers to electrical potential large enough to cause injury or damage. It's used in power transmission because it's more efficient to transport electricity over long distances at high voltages, reducing power loss. Examples include power lines and substations. Low voltage, on the other hand, is typically safe to touch and is commonly found in everyday devices like smartphones, tablets, and other personal gadgets.

Table 4:


High Voltage

Low Voltage

Voltage Range (generalized)

Above 1 kV (for alternating current systems)

Below 1 kV

Application Examples

Power transmission lines, substations, X-ray machines

Household appliances, electronics, lighting circuits

Insulation Requirements

Requires robust insulation and physical barriers

Basic insulation is often sufficient

Safety Considerations

Specialized training required, serious shock hazard

Less dangerous but still can pose risks

Equipment Size

Generally larger due to insulation and spacing needs

Compact and often integrated into various devices

Energy Loss

Lower current levels reduce I²R losses

Higher I²R losses relative to the energy being transmitted


More expensive due to insulation and safety equipment

Generally less expensive

Low voltage might also be dangerous!

DC and AC

Direct Current (DC) and Alternating Current (AC) are two fundamental types of electric current. DC flows continuously in one direction and is typically used in batteries, electronic systems, and devices. AC, conversely, periodically reverses its direction, resembling a wave. It's the type of electricity delivered to our homes and businesses, mainly because it can be transmitted over long distances with minimal loss.

Table 5:


Direct Current (DC)

Alternating Current (AC)


Constant flow of electric charge in one direction.

Electric charge changes direction periodically.

Graphical Representation

Steady, flat line (when stable).

Sinusoidal wave (for single-phase AC).

Voltage or Current Direction


Changes direction cyclically.


Batteries, solar panels, electronics, and some high-speed trains.

Most home appliances, power transmission, motors.

Transmission Losses

Typically higher for long distances compared to AC.

Less for long-distance due to ability to transform voltage easily.

Voltage Conversion

Requires electronic components like converters.

Can use transformers to easily step-up or step-down voltage.


Steady voltage can pose a continuous shock risk.

Changing direction can throw off and release a person, but higher voltages are very dangerous.

Device Polarity

Polarity matters (positive/negative terminals).

No polarity in standard AC circuits.

Energy Storage

Easily stored in batteries.

Not easily stored; usually converted from other forms.

Electrical and Electronics

Though often used interchangeably, "electrical" and "electronics" refer to distinct domains. Electrical generally concerns the large-scale production and distribution of power, such as power plants, transmission lines, and major appliances. Electronics, however, delves into the behavior and movement of electrons in semiconductors, dealing with small-scale circuits found in devices like radios, computers, and other digital gadgets. In essence, while electrical engineering encompasses broader systems, electronics focuses on intricate details of smaller components and circuits.

Table 6:





Study of the flow and behavior of electric charge.

Branch of technology and science dealing with circuits that manipulate and control the flow of electric current.


Broader term, encompassing any movement of charges.

Subset of electricity focusing on devices that control the movement, storage, and processing of information and energy.


Simple circuits, conductors, insulators, switches, etc.

Transistors, capacitors, ICs, diodes, resistors, etc.


Lighting, heating, simple electrical machines.

Computers, telecommunication, sensors, complex machines, consumer electronics.


Transmission and conversion of electrical energy.

Processing, control, and communication of electrical signals.


Can be straightforward in simple circuits.

Can be highly intricate, especially in integrated circuits and digital systems.

Systems Involved

Power generation, transmission, and distribution systems.

Audio and video systems, microcontrollers, embedded systems, etc.

Study Areas

Basic circuit laws, magnetism, generation systems.

Digital logic, analog circuits, signal processing, control systems.

Signal Nature

Mostly concerns power levels.

Concerned with both power and information signals.

Amplitude and Frequency

Amplitude and frequency are two primary characteristics of AC. Amplitude refers to the height of the wave or the maximum voltage level, representing the wave's strength. Frequency, measured in Hertz (Hz), indicates the number of cycles an AC waveform completes in one second. It determines the wave form's speed. For instance, the standard power line frequency in most countries is either 50 or 60 Hz.

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