Units of Measurement in Electronics – Where Did Measurement Units Come From and What Do They Mean?

Electronics is a field in which numerous physical quantities and fundamental units of measurement are used on a daily basis. They enable us to describe the operation of circuits, perform measurements, and design electronic devices. Among the most important concepts are electric voltage (V), electric current (A), electrical resistance, power, capacitance, and inductance.

It is worth noting that the modern SI units of measurement were not created by chance. Many of them are named after scientists who made significant contributions to the development of physics and electrical engineering. Today, most measurements are based on the International System of Units (SI), which standardizes both the base units and the derived units within the system.

What Is the SI System of Units?

The SI System (International System of Units) is the globally accepted system of measurement units used for measuring physical quantities. It was developed to ensure that measurement results are unambiguous and as comparable as possible worldwide.

The SI system is based on 7 base units: 

Based on these units, derived units are defined, for example:

• electric voltage – volt (V),
• power – watt (W),
• electrical resistance – ohm (Ω),
• capacitance – farad (F).

The SI system also uses prefixes, which make it easier to express very large and very small values, for example:

• kilo (k) = 1,000,
• mega (M) = 1,000,000,
• milli (m) = 0.001,
• micro (µ) = 0.000001,
• nano (n) = 0.000000001.

Example:

• 2 km = 2,000 m,
• 5 ms = 0.005 s,
• 3 MW = 3,000,000 W.

The SI system is currently the standard used in science, engineering, medicine, and most countries around the world, ensuring that everyone uses the same units when performing and comparing measurements.

Where Do the Names of Units Used in Electronics Come From?

Many units used in electronics and electrical engineering are named after distinguished scientists who made significant contributions to the advancement of electricity, magnetism, and electronics.

Amper (A) – André-Marie Ampère. French physicist, mathematician, and one of the founders of electrodynamics. He studied the relationship between electric current and magnetic fields.

Wolt (V) – Alessandro Volta. Italian physicist and inventor of the first electric battery, known as the voltaic pile. His research contributed significantly to the development of electrical engineering.

Om (Ω) – Georg Simon Ohm. German physicist and teacher. He formulated Ohm’s law, which describes the relationship between voltage, current, and resistance.

Wat (W) – James Watt. Scottish inventor and mechanical engineer. He improved the steam engine, contributing to the development of industry and power generation.

Farad (F) – Michael Faraday. English physicist and chemist. He discovered electromagnetic induction and established the foundations for the operation of transformers and electric motors.

Henr (H) – Joseph Henry. American physicist who studied electromagnetism. Independently of Faraday, he discovered electromagnetic induction and advanced the development of electromagnets.

Herc (Hz) – Heinrich Hertz. German physicist who was the first to experimentally confirm the existence of electromagnetic waves predicted by James Clerk Maxwell.

Kolumb (C) – Charles-Augustin de Coulomb. French physicist and military engineer. He studied the interactions between electric charges and formulated Coulomb’s law.

Tesla (T) – Nikola Tesla. Serbian-American inventor, electrical engineer, and mechanical engineer. He developed numerous technologies related to alternating current (AC), electric motors, and power transmission.

Base Units of the SI System:

1. Length

Unit: metre (m).

Definition: Defines the distance between two points and is used to describe the dimensions of an object.

Example: A pen has a length of 15 cm, which is equivalent to 0.15 m.

2. Mass

Unit: kilogram (kg).

Definition: Defines the amount of matter in an object, indicating how much mass it contains.

Example: A school bag has a mass of 5 kg.

3. Time

Unit: second (s).

Definition: Defines the duration of a phenomenon or the interval between events, allowing measurement of how long something lasts.

Example: A blink of an eye lasts approximately 0.3 s.

4. Electric Current

Unit: ampere (A).

Definition: Defines the amount of electric charge flowing through a conductor per unit of time and indicates the magnitude of the current flow.

Example: A current of 5 A flows through a conductor, meaning that a charge of 5 coulombs passes through it every second.

5. Thermodynamic Temperature

Unit: kelvin (K).

Definition: Defines the thermal state of an object and indicates how hot or cold it is.

Example: Room temperature is approximately 293 K (20°C).

6. Amount of Substance

Unit: mole (mol).

Definition: Defines the amount of substance by specifying the number of particles (atoms, molecules, etc.) it contains and is used to quantify extremely large numbers of microscopic entities.

Example: 1 mole of water contains approximately 6.02 × 10²³ water molecules.

7. Luminous Intensity

Unit: candela (cd).

Definition: Defines the luminous intensity of a light source in a given direction and indicates how brightly the source emits light.

Example: A lit candle has a luminous intensity of approximately 1 candela (1 cd).

What Is Electric Voltage (U)?

Simply put, electric voltage (U) is the force that drives electric current to flow through a circuit. It can be compared to water flowing through a pipe:

• electric current is like water flowing through the pipe,
• voltage is like the pressure that pushes the water through it.

The higher the pressure, the easier and faster the water flows. The same principle applies in electricity: the higher the voltage, the greater the potential to drive electric current through a circuit.

Example from everyday life: Imagine a balloon filled with air. If you make a small hole in it, the air will begin to escape because the pressure inside the balloon is higher than the pressure outside. Electric voltage works in a similar way: electrons move from a point of higher electric potential to a point of lower electric potential, creating an electric current flow.

What Is Voltage Measured In?

The unit of electric voltage is the volt (V).

Examples:

• AA battery – 1.5 V,
• USB port – 5 V,
• car battery – 12 V,
• household electrical outlet – 230 V.

Why Is Voltage Important?

Without voltage, electric current would have no driving force to flow. Voltage is what enables electrical devices to operate, including smartphones, laptops, televisions, refrigerators, and lighting systems.

Electric Voltage – How to Measure Voltage?

Electric voltage is measured using a voltmeter.

The meter is connected in parallel to the component or voltage source being tested. The measurement result is displayed in volts (V).

For example, to check the voltage of an AA battery, the voltmeter probes are placed on its terminals. The reading may be approximately 1.5 V.

Where Is Electric Current (I) Used?

Electric current defines the amount of electric charge flowing through a conductor within a specified period of time. It is one of the fundamental quantities used to describe electric current. The greater the flow of electric charges, the higher the current.

In practice, electric current flow can be compared to the flow of water through pipes. The more water that passes through a pipe in one second, the greater the flow rate. Similarly, the more electric charge that moves through a conductor during the same period, the higher the current.

The unit of electric current is the ampere (A). It is one of the seven base units of the SI system.

The term electric current in amperes is often used to refer to the measurement of current expressed in amperes. Understanding this quantity is essential wherever electrical measurements, electric current measurements, and the parameters of electronic devices are analyzed.

How to Measure Electric Current?

Electric current is measured using an ammeter. The meter is connected in series with the circuit so that the entire current flows through the measuring instrument. The measurement result is expressed in amperes (A).

Example: When charging a smartphone, it can be measured that the charger supplies a current of 2 A.

What Is Resistance (R) and Electrical Resistance?

Resistance (electrical resistance) defines how strongly a component opposes the flow of electric current.

The unit of electrical resistance is the ohm (Ω).

In practice, resistance is measured using a multimeter equipped with an ohmmeter function. A useful analogy for electrical resistance is a constriction in a pipe: a wide pipe allows water to flow easily, while a narrow pipe restricts the flow.

What Does Resistance Depend On?

The value of electrical resistance depends on several factors, including:

• the type of material (for example, copper conducts electricity more effectively than plastic),
• the length of the conductor,
• the cross-sectional area of the conductor,
• temperature.

Resistance makes it possible to control current flow in electrical circuits. It helps protect devices from damage and enables the regulation of various electronic components, such as LEDs, sensors, and integrated circuits.

Electrical Power (P) and Its Types

Power defines the rate at which electrical energy is consumed or transferred. The higher the power rating of a device, the more energy it consumes over the same period of time. For example, a 60 W light bulb consumes twice as much energy as a 30 W bulb during the same period.

In alternating current (AC) circuits, the following types of power are distinguished:

• Active power (performs work) – performs useful work and is converted into other forms of energy, such as light, heat, or motion.
• Reactive power (supports device operation) – does not perform useful work but is required for the operation of certain electrical devices, such as motors, transformers, and inductors. Simply put, it “circulates” between the power source and the load.
• Apparent power (the combination of both types of power) – the total power drawn from the electrical grid. It consists of active power and reactive power and indicates the overall loading of the electrical system.

What Is Capacitance?

Capacitance defines a capacitor’s ability to store energy and accumulate electric charge. In electronic circuits, capacitors are used for functions such as voltage filtering and stabilizing circuit operation. The unit of capacitance is the farad (F).

Capacitors are commonly used in:

• computer power supplies,
• phone chargers,
• camera flash units,
• electronic circuits in televisions and computers.

The greater the capacitance of a capacitor, the more energy it can store, and the more effectively it can stabilize voltage and reduce interference in an electrical circuit.

How Do Inductance and Magnetism Work?

Inductors store energy in a magnetic field. Their most important parameter is inductance. The unit of inductance is the henry (H), named after Joseph Henry.

In general, two concepts are commonly encountered:

Self-inductance – a coil interacts with itself and opposes changes in its own current.

Mutual inductance – one coil interacts with another coil, inducing a voltage in it.

The phenomena of self-inductance and mutual inductance are directly related to magnetic flux and the magnetic field. Magnetic flux defines the amount of magnetic field passing through a given surface, such as the turns of a coil. The unit used to describe magnetic flux density is the tesla (T).

What Is Frequency (f)?

The unit of frequency is the hertz (Hz).

Frequency defines how many times a given phenomenon repeats within one second. For example, the electric current supplied by household outlets in Poland has a frequency of 50 Hz, which means that the current changes direction 50 times per second.

 What Is Electric Charge Used For?

Electric charge describes the amount of charge stored or moving within a circuit. The proper movement of electric charges results in the flow of electric current. The total quantity of electric charge is expressed in coulombs. The coulomb (C) is the official unit of electric charge.

Electric charge plays a key role in:

• the operation of batteries and accumulators,
• the transmission of electrical energy,
• electronics and computers,
• capacitors used for charge storage,
• electrostatic phenomena such as lightning.

Summary

Measurements and units used in electronics make it possible to accurately describe the operation of electrical circuits and perform measurements correctly. Most of these units are based on the International System of Units (SI), which serves as the common standard used throughout science and engineering.

In electronics, particularly important quantities include electric voltage (V), electric current (A), resistance (Ω), power (W), capacitance (F), inductance (H), frequency (Hz), and electric charge (C). These quantities form the foundation for designing, commissioning, and troubleshooting electronic devices, ranging from simple circuits to advanced computer and power systems.

An understanding of the base units of measurement and their significance helps in comprehending the operation of electrical devices, correctly interpreting measurement results, and working safely with electronic circuits. It is fundamental knowledge for anyone interested in electronics, whether as a hobbyist or a professional.